hwmon: qpnp-vadc: Hold a lock during calibration

Calibration is performed during the first read request.
Have a lock around the calibration function to avoid
race condition of running into a scenario if two clients
issue an ADC request at the same time.

Change-Id: I0f7d0978da0179937b2d4699b4402c8666482cd0
Signed-off-by: Siddartha Mohanadoss <smohanad@codeaurora.org>
1 file changed