qemu-api: avoid build failure

* src/remote_protocol-structs: Tweak to match intentional type
change (with no ABI change) in remote protocol.

src/remote_protocol-structs

@@ -1308,7 +1308,7 @@ struct remote_domain_snapshot_delete_args {
 struct remote_message_header {
 	u_int                      prog;
 	u_int                      vers;
-	remote_procedure           proc;
+	int                        proc;
 	remote_message_type        type;
 	u_int                      serial;
 	remote_message_status      status;