drivers/rtc/rtc-hid-sensor-time.c: improve error handling when rtc register fails

Stop processing hid input when registering the RTC fails and handle a NULL
returned from devm_rtc_device_register() as a failure too.

Signed-off-by: Alexander Holler <holler@ahsoftware.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>