rtc: pm8xxx: Fix issue in RTC write path

[ Upstream commit 83220bf38b77a830f8e62ab1a0d0408304f9b966 ]

In order to set time in rtc, need to disable
rtc hw before writing into rtc registers.

Also fixes disabling of alarm while setting
rtc time.

Signed-off-by: Mohit Aggarwal <maggarwa@codeaurora.org>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>