crypto/sm2/sm2_sign.c: ensure UINT16_MAX is properly defined

Fixes #7186
Reviewed-by: NTim Hudson <tjh@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/7193)

(cherry picked from commit 88ea3685e4bf30fc529fe46e19effc6317726de8)

crypto/sm2/sm2_sign.c

@@ -12,6 +12,7 @@
 #include "internal/sm2.h"
 #include "internal/sm2err.h"
 #include "internal/ec_int.h" /* ec_group_do_inverse_ord() */
+#include "internal/numbers.h"
 #include <openssl/err.h>
 #include <openssl/evp.h>
 #include <openssl/err.h>