CIFS: fix sha512 check in cifs_crypto_secmech_release

It seems this is a copy-paste error and that the proper variable to use
in this particular case is _sha512_ instead of _md5_.

Addresses-Coverity-ID: 1465358 ("Copy-paste error")
Fixes: 1c6614d229e7 ("CIFS: add sha512 secmech")
Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Reviewed-by: Aurelien Aptel <aaptel@suse.com>
CC: Stable <stable@vger.kernel.org>
Signed-off-by: Steve French <smfrench@gmail.com>

fs/cifs/cifsencrypt.c

@@ -829,7 +829,7 @@ cifs_crypto_secmech_release(struct TCP_Server_Info *server)
 		server->secmech.md5 = NULL;
 	}
 
-	if (server->secmech.md5) {
+	if (server->secmech.sha512) {
 		crypto_free_shash(server->secmech.sha512);
 		server->secmech.sha512 = NULL;
 	}