rtc: qpnp-rtc: Set alarm control register properly

RTC Alarm enable bit does not get conserved during
RTC probe function. This patch fixes that issue.

Change-Id: I28203b8e301510d34d2e726c0bd25e78737f7524
CRs-Fixed: 636652
Signed-off-by: Mohit Aggarwal <maggarwa@codeaurora.org>