rtc: tps65910: fix typo in register name in read_alarm()

Fix an obvious typo: in read_alarm() call we should read alarm setting
(starting at ALARM_SECONDS register) and not current time.

Signed-off-by: Michał Mirosław <mirq-linux@rere.qmqm.pl>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>