Merge pull request #283 from ARMmbed/dev/gilles-peskine-arm/ctr_drbg-aes_fail-crypto

Uncaught AES failure in CTR_DRBG
diff --git a/library/ctr_drbg.c b/library/ctr_drbg.c
index 047bb2a..517b455 100644
--- a/library/ctr_drbg.c
+++ b/library/ctr_drbg.c
@@ -584,7 +584,7 @@
 exit:
     mbedtls_platform_zeroize( add_input, sizeof( add_input ) );
     mbedtls_platform_zeroize( tmp, sizeof( tmp ) );
-    return( 0 );
+    return( ret );
 }
 
 int mbedtls_ctr_drbg_random( void *p_rng, unsigned char *output,