power: pm8xxx-ccadc: missing calibration at bootup

There is a bug in the sequence between when the calibration work is
scheduled and the global chip pointer is initialized. If work is
scheduled before the chip pointer is initialized it refuses to
calibrate.

Initialize the chip pointer before scheduling calibration work.

Change-Id: I333c97c005e8bc17a28fc0dac3f76e4f26fcc486
Signed-off-by: Abhijeet Dharmapurikar <adharmap@codeaurora.org>