thermal: ti-soc-thermal: bandgap: Fix build warning if !CONFIG_PM_SLEEP

Fix following build warning if CONFIG_PM_SLEEP is not set:

drivers/thermal/ti-soc-thermal/ti-bandgap.c:1478:12: warning: 'ti_bandgap_suspend' defined but not used [-Wunused-function]
 static int ti_bandgap_suspend(struct device *dev)
            ^
drivers/thermal/ti-soc-thermal/ti-bandgap.c:1492:12: warning: 'ti_bandgap_resume' defined but not used [-Wunused-function]
 static int ti_bandgap_resume(struct device *dev)
            ^
Acked-by: Nishanth Menon <nm@ti.com>
Signed-off-by: Grygorii Strashko <Grygorii.Strashko@linaro.org>
Signed-off-by: Eduardo Valentin <edubezval@gmail.com>