rtc: rx8025: fix 12/24 hour mode detection on RX-8035

The 12/24hr flag in the RX-8035 can be found in the hour register,
instead of the CTRL1 on the RX-8025. This was overlooked when
support for the RX-8035 was added, and was causing read errors when
the hour register 'overflowed'.

To deal with the relevant register not always being visible in
the relevant functions, determine the 12/24 mode at startup and
store it in the driver state.

Signed-off-by: Mathew McBride <matt@traverse.com.au>
Fixes: f120e2e3 ("rtc: rx8025: implement RX-8035 support")
Cc: stable@vger.kernel.org
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Link: https://lore.kernel.org/r/20220706074236.24011-1-matt@traverse.com.au