regulator: dbx500: Make local symbol static

power_state_active_get is used only in this file. Make it static.
While at it also move this function definition inside the
CONFIG_REGULATOR_DEBUG macro as it is called only from within it.
This also avoids further build warning related to unused definition.

Signed-off-by: Sachin Kamat <sachin.kamat@linaro.org>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>