rtc: ds1511: drop useless computation

All the callers of ds1511_rtc_set_time will use the same epoch for tm_year
which is defined as the number of years minus 1900 since POSIX.1-2001.

Link: https://lore.kernel.org/r/20240227230431.1837717-2-alexandre.belloni@bootlin.com


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