mc146818rtc: update registers after a format change

mc146818rtc: update registers after a format change

For some unknown reason, the MIPS kernel briefly changes the RTC to
binary mode during boot, switch back to BCD mode and read the time. As
the registers are updated only every second, they may still be in the
old format when they are read.

This patch forces a register update immediately after a format change
(BCD/binary or 12/24H). This avoid long fsck during boot due to time
wrap.

Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>