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: d4b675e1 ("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>