Replaced mbedtls_ssl_safer_memcmp with mbedtls_platform_memcmp

Saves some bytes and mbedtls_platform_memcmp is a bit safer for side channel
attacks.
diff --git a/library/asn1write.c b/library/asn1write.c
index 0ec1647..5c11796 100644
--- a/library/asn1write.c
+++ b/library/asn1write.c
@@ -28,12 +28,12 @@
 #if defined(MBEDTLS_ASN1_WRITE_C)
 
 #include "mbedtls/asn1write.h"
+#include "mbedtls/platform_util.h"
 
 #include <string.h>
 
 #if defined(MBEDTLS_PLATFORM_C)
 #include "mbedtls/platform.h"
-#include "mbedtls/platform_util.h"
 #else
 #include <stdlib.h>
 #define mbedtls_calloc    calloc