vcs: make proper usage of the poll flags

Kay Sievers pointed out that usage of POLLIN is well defined by POSIX,
and the current usage here doesn't follow that definition.  So let's
duplicate the same semantics as implemented by sysfs_poll() instead.
Signed-off-by: Nicolas Pitre <nicolas.pitre@canonical.com>
Acked-by: Kay Sievers <kay.sievers@vrfy.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/tty/vt/vc_screen.c

@@ -553,12 +553,12 @@ static unsigned int
 vcs_poll(struct file *file, poll_table *wait)
 {
 	struct vcs_poll_data *poll = vcs_poll_data_get(file);
-	int ret = 0;
+	int ret = DEFAULT_POLLMASK|POLLERR|POLLPRI;
 
 	if (poll) {
 		poll_wait(file, &poll->waitq, wait);
-		if (!poll->seen_last_update)
-			ret = POLLIN | POLLRDNORM;
+		if (poll->seen_last_update)
+			ret = DEFAULT_POLLMASK;
 	}
 	return ret;
 }