power: pm8xxx-ccadc: reduce boot time for calibration

- reduce the wait time between adc readings to 20ms from 60ms. This
  speeds up the calibration time.

- move the initial calibration to a workqueue.

CRs-Fixed: 331215
Change-Id: I2034c55f2df8d3e1df216dd5a739cbe70e53c2ed
Signed-off-by: Abhijeet Dharmapurikar <adharmap@codeaurora.org>
2 files changed