hwmon: qpnp-adc: Remove calibration in vadc_hc_read

Software calibration is not required in hardware calibrated
peripheral. Remove calibration call in voltage read function
for hardware calibrated peripheral.

Change-Id: Icb311db384221b801207b2063c33545e4ba6b27f
Signed-off-by: Jishnu Prakash <jprakash@codeaurora.org>