Apply review feedback on ECP interface

Naming conventions are revised, style issues corrected and minor
optimisation added.
diff --git a/library/threading.c b/library/threading.c
index b0cebd1..81c1075 100644
--- a/library/threading.c
+++ b/library/threading.c
@@ -113,8 +113,8 @@
 
     mbedtls_mutex_init( &mbedtls_threading_readdir_mutex );
     mbedtls_mutex_init( &mbedtls_threading_gmtime_mutex );
-#if defined(MBEDTLS_ECP_FUNCTION_ALT)
-    mbedtls_mutex_init( &mbedtls_threading_cryptohw_asym_mutex );
+#if defined(MBEDTLS_ECP_INTERNAL_ALT)
+    mbedtls_mutex_init( &mbedtls_threading_ecp_mutex );
 #endif
 }
 
@@ -125,8 +125,8 @@
 {
     mbedtls_mutex_free( &mbedtls_threading_readdir_mutex );
     mbedtls_mutex_free( &mbedtls_threading_gmtime_mutex );
-#if defined(MBEDTLS_ECP_FUNCTION_ALT)
-    mbedtls_mutex_free( &mbedtls_threading_cryptohw_asym_mutex );
+#if defined(MBEDTLS_ECP_INTERNAL_ALT)
+    mbedtls_mutex_free( &mbedtls_threading_ecp_mutex );
 #endif
 }
 #endif /* MBEDTLS_THREADING_ALT */
@@ -139,8 +139,8 @@
 #endif
 mbedtls_threading_mutex_t mbedtls_threading_readdir_mutex MUTEX_INIT;
 mbedtls_threading_mutex_t mbedtls_threading_gmtime_mutex MUTEX_INIT;
-#if defined(MBEDTLS_ECP_FUNCTION_ALT)
-mbedtls_threading_mutex_t mbedtls_threading_cryptohw_asym_mutex MUTEX_INIT;
+#if defined(MBEDTLS_ECP_INTERNAL_ALT)
+mbedtls_threading_mutex_t mbedtls_threading_ecp_mutex MUTEX_INIT;
 #endif
 
 #endif /* MBEDTLS_THREADING_C */