hwmon: qpnp-adc: Remove interrupt initialization

The SPMI peripheral driver is not required to initialize
the peripheral interrupts. The QPNP interrupt driver
handles setting the configuration for the corresponding
interrupt bit for which the peripheral driver makes a request.

Remove the free_irq for voltage irq in the failure path.
The request is made through devm_request_irq and it will
handle freeing the irq.

Change-Id: Ie0b416d39dfe9a9811f5e21512413b62c6db27de
Signed-off-by: Siddartha Mohanadoss <smohanad@codeaurora.org>