thermal: tsens: Update variable type

From the logic implemented, there is a chance that sensor_hw_num
can get a negative value. Update type of sensor_hw_num such that
it can hold both positive and negative values.

Change-Id: Ib05aedea90bc5797140728b6e64f15e5c11f9b25
Signed-off-by: Rama Krishna Phani A <rphani@codeaurora.org>