Add MBEDTLS_CHECK_RETURN_CRITICAL annotation

Ensure that the compiler will warn us if we do not check the
return of calc_verify in future.

Signed-off-by: David Horstmann <david.horstmann@arm.com>

include/mbedtls/ssl_internal.h

@@ -467,6 +467,7 @@ struct mbedtls_ssl_handshake_params {
 
     void (*update_checksum)(mbedtls_ssl_context *, const unsigned char *, size_t);
     void (*calc_verify)(const mbedtls_ssl_context *, unsigned char *, size_t *);
+    MBEDTLS_CHECK_RETURN_CRITICAL
     int (*calc_finished)(mbedtls_ssl_context *, unsigned char *, int);
     mbedtls_ssl_tls_prf_cb *tls_prf;