msm: cpr-regulator: change the sequence for handling corner switch

Clear all of the CPR control and configuration registers before switching
to a new voltage corner and then restore their values after corner
switching is complete. This sequence ensures that spurious up or down
interrupts are not received when CPR is re-enabled after corner switching
is complete.

Change-Id: I646c747c9bfa7474bd421074dc2f6e2b28ef347c
CRs-Fixed: 604782
Signed-off-by: Ke Liu <keliu@codeaurora.org>