Input: samsung-keypad - don't synchronise with runtime PM put

We don't actually care if the device has been runtime suspended immediately
so we can just drop the reference without waiting for any state change to
be implemented. This may allow us to avoid some suspend/resume cycles and
is a bit more friendly to the rest of the system.

Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>