thermal/drivers/tsens: Fix compilation warnings by making functions static

thermal/drivers/tsens: Fix compilation warnings by making functions static

After merging tsens-common.c into tsens.c, we can now mark some
functions static so they don't need any prototype declarations. This
fixes the following issue reported by lkp.

>> drivers/thermal/qcom/tsens.c:385:13: warning: no previous prototype for 'tsens_critical_irq_thread' [-Wmissing-prototypes]
385 | irqreturn_t tsens_critical_irq_thread(int irq, void *data)
|             ^~~~~~~~~~~~~~~~~~~~~~~~~
>> drivers/thermal/qcom/tsens.c:455:13: warning: no previous prototype for 'tsens_irq_thread' [-Wmissing-prototypes]
455 | irqreturn_t tsens_irq_thread(int irq, void *data)
|             ^~~~~~~~~~~~~~~~
>> drivers/thermal/qcom/tsens.c:523:5: warning: no previous prototype for 'tsens_set_trips' [-Wmissing-prototypes]
523 | int tsens_set_trips(void *_sensor, int low, int high)
|     ^~~~~~~~~~~~~~~
>> drivers/thermal/qcom/tsens.c:560:5: warning: no previous prototype for 'tsens_enable_irq' [-Wmissing-prototypes]
560 | int tsens_enable_irq(struct tsens_priv *priv)
|     ^~~~~~~~~~~~~~~~
>> drivers/thermal/qcom/tsens.c:573:6: warning: no previous prototype for 'tsens_disable_irq' [-Wmissing-prototypes]
573 | void tsens_disable_irq(struct tsens_priv *priv)
|      ^~~~~~~~~~~~~~~~~

Signed-off-by: Amit Kucheria <amit.kucheria@linaro.org>
Reported-by: kbuild test robot <lkp@intel.com>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Link: https://lore.kernel.org/r/6757a26876b29922929abf64b1c11fa3b3033d03.1590579709.git.amit.kucheria@linaro.org