CTR_DRBG: Don't use functions before they're defined

Move the definitions of mbedtls_ctr_drbg_seed_entropy_len() and
mbedtls_ctr_drbg_seed() to after they are used. This makes the code
easier to read and to maintain.
diff --git a/library/ctr_drbg.c b/library/ctr_drbg.c
index d7a9484..a99ec00 100644
--- a/library/ctr_drbg.c
+++ b/library/ctr_drbg.c
@@ -66,56 +66,6 @@
 #endif
 }
 
-/*
- * Non-public function wrapped by mbedtls_ctr_drbg_seed(). Necessary to allow
- * NIST tests to succeed (which require known length fixed entropy)
- */
-int mbedtls_ctr_drbg_seed_entropy_len(
-                   mbedtls_ctr_drbg_context *ctx,
-                   int (*f_entropy)(void *, unsigned char *, size_t),
-                   void *p_entropy,
-                   const unsigned char *custom,
-                   size_t len,
-                   size_t entropy_len )
-{
-    int ret;
-    unsigned char key[MBEDTLS_CTR_DRBG_KEYSIZE];
-
-    memset( key, 0, MBEDTLS_CTR_DRBG_KEYSIZE );
-
-    mbedtls_aes_init( &ctx->aes_ctx );
-
-    ctx->f_entropy = f_entropy;
-    ctx->p_entropy = p_entropy;
-
-    ctx->entropy_len = entropy_len;
-    ctx->reseed_interval = MBEDTLS_CTR_DRBG_RESEED_INTERVAL;
-
-    /*
-     * Initialize with an empty key
-     */
-    if( ( ret = mbedtls_aes_setkey_enc( &ctx->aes_ctx, key, MBEDTLS_CTR_DRBG_KEYBITS ) ) != 0 )
-    {
-        return( ret );
-    }
-
-    if( ( ret = mbedtls_ctr_drbg_reseed( ctx, custom, len ) ) != 0 )
-    {
-        return( ret );
-    }
-    return( 0 );
-}
-
-int mbedtls_ctr_drbg_seed( mbedtls_ctr_drbg_context *ctx,
-                   int (*f_entropy)(void *, unsigned char *, size_t),
-                   void *p_entropy,
-                   const unsigned char *custom,
-                   size_t len )
-{
-    return( mbedtls_ctr_drbg_seed_entropy_len( ctx, f_entropy, p_entropy, custom, len,
-                                       MBEDTLS_CTR_DRBG_ENTROPY_LEN ) );
-}
-
 void mbedtls_ctr_drbg_free( mbedtls_ctr_drbg_context *ctx )
 {
     if( ctx == NULL )
@@ -386,6 +336,56 @@
     return( ret );
 }
 
+/*
+ * Non-public function wrapped by mbedtls_ctr_drbg_seed(). Necessary to allow
+ * NIST tests to succeed (which require known length fixed entropy)
+ */
+int mbedtls_ctr_drbg_seed_entropy_len(
+                   mbedtls_ctr_drbg_context *ctx,
+                   int (*f_entropy)(void *, unsigned char *, size_t),
+                   void *p_entropy,
+                   const unsigned char *custom,
+                   size_t len,
+                   size_t entropy_len )
+{
+    int ret;
+    unsigned char key[MBEDTLS_CTR_DRBG_KEYSIZE];
+
+    memset( key, 0, MBEDTLS_CTR_DRBG_KEYSIZE );
+
+    mbedtls_aes_init( &ctx->aes_ctx );
+
+    ctx->f_entropy = f_entropy;
+    ctx->p_entropy = p_entropy;
+
+    ctx->entropy_len = entropy_len;
+    ctx->reseed_interval = MBEDTLS_CTR_DRBG_RESEED_INTERVAL;
+
+    /*
+     * Initialize with an empty key
+     */
+    if( ( ret = mbedtls_aes_setkey_enc( &ctx->aes_ctx, key, MBEDTLS_CTR_DRBG_KEYBITS ) ) != 0 )
+    {
+        return( ret );
+    }
+
+    if( ( ret = mbedtls_ctr_drbg_reseed( ctx, custom, len ) ) != 0 )
+    {
+        return( ret );
+    }
+    return( 0 );
+}
+
+int mbedtls_ctr_drbg_seed( mbedtls_ctr_drbg_context *ctx,
+                   int (*f_entropy)(void *, unsigned char *, size_t),
+                   void *p_entropy,
+                   const unsigned char *custom,
+                   size_t len )
+{
+    return( mbedtls_ctr_drbg_seed_entropy_len( ctx, f_entropy, p_entropy, custom, len,
+                                       MBEDTLS_CTR_DRBG_ENTROPY_LEN ) );
+}
+
 int mbedtls_ctr_drbg_random_with_add( void *p_rng,
                               unsigned char *output, size_t output_len,
                               const unsigned char *additional, size_t add_len )