Input: uinput - always report EPOLLOUT

uinput device is always available for writing so we should always report
EPOLLOUT and EPOLLWRNORM bits, not only when there is nothing to read from
the device.

Fixes: d4b675e ("Input: uinput - fix returning EPOLLOUT from uinput_poll")
Reported-by: Linus Torvalds <torvalds@linux-foundation.org>
Link: https://lore.kernel.org/r/20191209202254.GA107567@dtor-ws
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>

drivers/input/misc/uinput.c

@@ -689,13 +689,14 @@ static ssize_t uinput_read(struct file *file, char __user *buffer,
 static __poll_t uinput_poll(struct file *file, poll_table *wait)
 {
 	struct uinput_device *udev = file->private_data;
+	__poll_t mask = EPOLLOUT | EPOLLWRNORM; /* uinput is always writable */
 
 	poll_wait(file, &udev->waitq, wait);
 
 	if (udev->head != udev->tail)
-		return EPOLLIN | EPOLLRDNORM;
+		mask |= EPOLLIN | EPOLLRDNORM;
 
-	return EPOLLOUT | EPOLLWRNORM;
+	return mask;
 }
 
 static int uinput_release(struct inode *inode, struct file *file)