thermal: tsens: Get rid of dead code

hw_id is dynamically allocated but not used anywhere. Get rid of dead
code.

Signed-off-by: Amit Kucheria <amit.kucheria@linaro.org>
Reviewed-by: Matthias Kaehlcke <mka@chromium.org>
Reviewed-by: Bjorn Andersson <bjorn.andersson@linaro.org>