rtc: sun6i: switch to rtc_time64_to_tm/rtc_tm_to_time64

Call the 64bit versions of rtc_tm time conversion.

Tested-by: Paul Kocialkowski <paul.kocialkowski@bootlin.com>
Link: https://lore.kernel.org/r/20200330201226.860967-2-alexandre.belloni@bootlin.com


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