rtc: ds1347: mask ALM OUT when reading time

Bit 7 of the minutes registers is ALM OUT. It indicates an alarm fired.
Mask it out when reading the time.

Link: https://lore.kernel.org/r/20191007134724.15505-5-alexandre.belloni@bootlin.com


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