The driver was reading the wrong register as the 10-hour digit due to
a misplaced ')'. It was in fact reading the 1-second digit register due
to this bug.

Also remove the use of a magic number for the hour mask and use the define
for it which was already present.

Fixes: 4f9b9bba ("rtc: Add an RTC driver for the Oki MSM6242")
Tested-by: Kars de Jong <jongk@linux-m68k.org>
Signed-off-by: Kars de Jong <jongk@linux-m68k.org>
Link: https://lore.kernel.org/r/20191116110548.8562-1-jongk@linux-m68k.orgReviewed-by: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>