rtc: sh: drop bogus assignment of tm_year in .read_alarm

This rtc doesn't support triggering on years, so don't assign tm_year
instead of claiming the alarm is to trigger in year 67435.

Signed-off-by: Uwe Kleine-König <uwe@kleine-koenig.org>
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>