power: pm8xxx-ccadc: fix incorrect offset value

A race condition exists where an interrupt could trigger as soon as
it is requested, causing uninitialized data to be written in the offset
trim registers.

Fix this by initializing the offset values before requesting the interrupt.
Also keep the interrupt disabled, the driver enables them only when it
needs to use it.

Signed-off-by: Abhijeet Dharmapurikar <adharmap@codeaurora.org>
Change-Id: I69690f64b599f56f7beaf6854061b2a54da44148