Fix incorrect return style

Signed-off-by: David Horstmann <david.horstmann@arm.com>
diff --git a/library/x509.c b/library/x509.c
index 812eba8..199f82b 100644
--- a/library/x509.c
+++ b/library/x509.c
@@ -552,7 +552,7 @@
 
     mbedtls_platform_zeroize( head, sizeof( *head ) );
 
-    return ret;
+    return( ret );
 }
 
 static int x509_parse_int( unsigned char **p, size_t n, int *res )