Input: stop autorepeat timer on key release

Whenever you press and then release a key, the CPU wakes up
three times:
 * press
 * release
 * autorepeat timer exactly 250ms after press

The autorepeat timer has nothing to do, obviously, since you already
have released the key, so stop it on key release.

[dtor@mail.ru: This changes autorepeat behavior a bit since we now stop
 autorepeat even if key that is being released is not the one that is
 being auto-repeated, but I believe the new behavior is better.]

Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>