seccomp: fix poor type promotion

sparse complains,

kernel/seccomp.c:1172:13: warning: incorrect type in assignment (different base types)
kernel/seccomp.c:1172:13:    expected restricted __poll_t [usertype] ret
kernel/seccomp.c:1172:13:    got int
kernel/seccomp.c:1173:13: warning: restricted __poll_t degrades to integer

Instead of assigning this to ret, since we don't use this anywhere, let's
just test it against 0 directly.
Signed-off-by: Tycho Andersen <tycho@tycho.ws>
Reported-by: 0day robot <lkp@intel.com>
Fixes: 6a21cc50 ("seccomp: add a return code to trap to userspace")
Signed-off-by: Kees Cook <keescook@chromium.org>

kernel/seccomp.c

@@ -1169,8 +1169,7 @@ static __poll_t seccomp_notify_poll(struct file *file,
 
 	poll_wait(file, &filter->notif->wqh, poll_tab);
 
-	ret = mutex_lock_interruptible(&filter->notify_lock);
-	if (ret < 0)
+	if (mutex_lock_interruptible(&filter->notify_lock) < 0)
 		return EPOLLERR;
 
 	list_for_each_entry(cur, &filter->notif->notifications, list) {