backlight: backlight: Slighly simplify devm_of_find_backlight()

Use devm_add_action_or_reset() instead of devm_add_action()+hand writing
what is done in the release function, should an error occur.

This is more straightforward and saves a few lines of code.

While at it, remove a useless test in devm_backlight_release(). 'data' is
known to be not NULL when this function is called.

Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Reviewed-by: Daniel Thompson <daniel.thompson@linaro.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Link: https://lore.kernel.org/r/f998a4291d865273afa0d1f85764a9ac7fbc1b64.1644738084.git.christophe.jaillet@wanadoo.fr