mfd: axp20x: Use devm_register_power_off_handler()

Simplify the code a bit by using devm_register_power_off_handler(), which is
a purpose-specific wrapper for devm_register_sys_off_handler().  No intended
functional changes are introduced.

Signed-off-by: Dragan Simic <dsimic@manjaro.org>
Link: https://lore.kernel.org/r/ab1f059f4b5bef75da3d3903d0fbf28bddffd57c.1731415409.git.dsimic@manjaro.org


Signed-off-by: Lee Jones <lee@kernel.org>