thermal: qpnp-adc-tm: Update High/Low ISR functions

Dual interrupts are observed by disabling the interrupts
in the workqueue, hence implement the logic in ISR handler.
Disable Low/High threshold interrupt along with disabling
the VADC peripheral within the ISR handler.

Change-Id: Ia0708b33d8dac24cbee96fa2ce679b1c4571b879
Signed-off-by: Rama Krishna Phani A <rphani@codeaurora.org>