power: pm8xxx-ccadc: remove sanity checks for ccadc calibration

Currently the code checks that the voltage readings for 0volts and
25mV are within a certain range. If it falls outside this range, the
code limits the value.

This limiting leads to error in calculating the battery current. Remove
the checks.

Change-Id: I581a45fe2f1fa8853a597e6ffdfefc7671d19f51
Signed-off-by: Abhijeet Dharmapurikar <adharmap@codeaurora.org>