Input: twl4030-pwrbutton - ensure a wakeup event is recorded.

This button is treated as a wakeup source, so we need to initialise it
correctly.

Without the device_init_wakeup() call, dev->power.wakeup will
be NULL, and pm_wakeup_event() will do nothing.

Signed-off-by: NeilBrown <neilb@suse.de>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>