hwmon: qpnp-adc: Fix blocking call at qpnp_vadc_calib()

Fix issue when a call to qpnp_vadc_calib() does not
return due to the end of conversion status bits not
being set. Add a count check while reading the status
registers instead of waiting forever till the end of
conversion bits get set. Also make changes in the IADC
driver to schedule work for calibration when there
are no errors. Previously we wanted to give a couple
of re-tries but once the calibration error occurs we
have seen it fail continously so there is no need to
have retries.

Change-Id: I5f994f38fbeb0a044146174d4189b1cd95fd040e
Signed-off-by: Siddartha Mohanadoss <smohanad@codeaurora.org>