mfd: db8500-prcmu: Remove unused inline function

commit b0e84624

 ("mfd: db8500-prcmu: Remove dead code for a non-existing config")
left behind this, remove it.

Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Link: https://lore.kernel.org/r/20220311125518.31064-1-yuehaibing@huawei.com