Input: hp_sdc_rtc should depend on serio

Fix this build error when CONFIG_SERIO is not set
hp_sdc_rtc.c:691: undefined reference to `hp_sdc_request_timer_irq'
and so on..

"select should be used with care. select will force
a symbol to a value without visiting the dependencies."

Signed-off-by: Alexander Beregalov <a.beregalov@gmail.com>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>