rtc: ds1511: drop useless checks

The RTC core will always pass a valid rtc_tm, it is unnecessary to check
the validity of its members, especially with an open coded version of
rtc_valid_tm().

Link: https://lore.kernel.org/r/20240227230431.1837717-1-alexandre.belloni@bootlin.com


Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>