hwmon: qpnp-adc: Correct return statement in VADC HC read API

Remove return statement in case of failure to write to calibration
peripheral and replace with goto statement to ensure mutex is released.

Change-Id: Iea91c80f5049d4ad7cb43a9ce8e7338ad522624d
Signed-off-by: Jishnu Prakash <jprakash@codeaurora.org>