mfd: palmas: Remove redundant check in palmas_power_off

palmas_dev and palmas_power_off are always assigned together.
So the check for palmas_dev inside palmas_power_off function
is redundant. Removing the same.

Signed-off-by: Keerthy <j-keerthy@ti.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>