msm: krait-regulator: fix PMIC voltage set point calculation

The current code assumes that there is a 80mV offset in the voltage
control definitions - before setting the pmic voltage it subtracts
80mV and then divides the result by 5mV step to get the voltage.

There is no offset in the register definition. Simply divide the
requested voltage by 5mV step.

Change-Id: I18b782338d05ef6ac8f28cc80a8c561b200aab14
Signed-off-by: Abhijeet Dharmapurikar <adharmap@codeaurora.org>