rtc: ds1347: fix value written to century register

In `ds1347_set_time()`, the wrong value is being written to the
`DS1347_CENTURY_REG` register.  It needs to be converted to BCD.  Fix
it.

Fixes: 147dae76 ("rtc: ds1347: handle century register")
Cc: <stable@vger.kernel.org> # v5.5+
Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Link: https://lore.kernel.org/r/20221027163249.447416-1-abbotti@mev.co.uk


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