Fix wrong register use when set/reset ST bit.
ST bit is in register M41T62_REG_SEC not in M41T62_REG_ALARM_HOUR.
I have not actually tested this. But this seemed buggy from inspection.
Fixes: 9bbe210512 ("rtc: m41t62: add oscillator fail bit reset support")
Signed-off-by: Max Yang <max.yang@deltaww.com>