rtc: mx27rtc: remove redundant code in rtc_reset

As of commit 1a1fa240 ("rtc: Set valid date after reset") the
command "date reset" will set the date/time to 2000-01-01 0:00:00 after
calling rtc_reset(). This means that the mx27rtc implementation of
rtc_reset() can be an empty stub function.

Signed-off-by: Chris Packham <judge.packham@gmail.com>