Input: gpio-keys - simplify argument list for report_event

For now this only saves a few instructions (for gpio_keys_report_event,
gpio_keys_isr and gpio_check_button one instraction each on ARM using
arm-linux-gnu-gcc 4.2.3---I assume this is similar for other arch/compiler
combinations).

Signed-off-by: Uwe Kleine-König <Uwe.Kleine-Koenig@digi.com>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>