rtc: m41t62: fix wrong register use for set/reset ST bit

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: 9bbe2105 ("rtc: m41t62: add oscillator fail bit reset support")
Signed-off-by: Max Yang <max.yang@deltaww.com>