Fix merge issue from 1.3 branch
diff --git a/library/entropy_poll.c b/library/entropy_poll.c
index aff52ba..ae3929a 100644
--- a/library/entropy_poll.c
+++ b/library/entropy_poll.c
@@ -145,7 +145,7 @@
         int ret;
 
         if( ( ret = getrandom_wrapper( output, len, 0 ) ) < 0 )
-            return( POLARSSL_ERR_ENTROPY_SOURCE_FAILED );
+            return( MBEDTLS_ERR_ENTROPY_SOURCE_FAILED );
 
         *olen = ret;
         return( 0 );