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/include/mbedtls/compat-1.3.h b/include/mbedtls/compat-1.3.h
index a58b4724..6e0fb8d 100644
--- a/include/mbedtls/compat-1.3.h
+++ b/include/mbedtls/compat-1.3.h
@@ -2231,7 +2231,7 @@
 #define rsa_rsassa_pss_verify_ext mbedtls_rsa_rsassa_pss_verify_ext
 #define rsa_self_test mbedtls_rsa_self_test
 #define rsa_set_padding mbedtls_rsa_set_padding
-#define safer_memcmp mbedtls_ssl_safer_memcmp
+#define safer_memcmp mbedtls_platform_memcmp
 #define set_alarm mbedtls_set_alarm
 #define sha1 mbedtls_sha1
 #define sha1_context mbedtls_sha1_context