backlight: lcd: Rearrange code in fb_notifier_callback()

backlight: lcd: Rearrange code in fb_notifier_callback()

First acquire the ops_lock and do all tests while holding it. Rearranges
the code in lcd's fb_notifier_callback() to resemble the callback in
the backlight module. This will simplify later changes to these tests.

v2:
- avoid gotos by using guard(mutex) (Daniel)
- fix typos in commit description (Daniel)

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Daniel Thompson <daniel.thompson@linaro.org>
Link: https://lore.kernel.org/r/20240906075439.98476-2-tzimmermann@suse.de
Signed-off-by: Lee Jones <lee@kernel.org>