regulator: db8500-prcmu: Remove unused declaration power_state_active_is_enabled()

Commit 38e96838 ("regulators/db8500: split off shared dbx500 code")
removed this but not its declaration.

Signed-off-by: Yue Haibing <yuehaibing@huawei.com>
Link: https://lore.kernel.org/r/20230818124227.15084-1-yuehaibing@huawei.com


Signed-off-by: Mark Brown <broonie@kernel.org>