HID: uhid: Fix returning EPOLLOUT from uhid_char_poll

HID: uhid: Fix returning EPOLLOUT from uhid_char_poll

BugLink: https://bugs.launchpad.net/bugs/1860131
commit be54e7461ffdc5809b67d2aeefc1ddc9a91470c7 upstream.

Always return EPOLLOUT from uhid_char_poll to allow polling /dev/uhid
for writable state.

Fixes: 1f9dec1e0164 ("HID: uhid: allow poll()'ing on uhid devices")
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>
Cc: stable@vger.kernel.org
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Paolo Pisati <paolo.pisati@canonical.com>