rtc: treewide: remove excess rtc_device validation

The patch "rtc: verify a critical argument to rtc_update_irq() before
using it" introduces validation for rtc_device in the RTC core, so there
are no need to check this argument for rtc_update_irq() from the
drivers.

This patch removes such check for the existing rtc_update_irq() users.

Signed-off-by: Alexander Shiyan <shc_work@mail.ru>
Cc: Alessandro Zummo <a.zummo@towertech.it>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>