backlight: omap1: Remove unused struct omap_backlight_config.set_power

backlight: omap1: Remove unused struct omap_backlight_config.set_power

The callback set_power in struct omap_backlight_config is not
implemented anywhere. Remove it from the structure and driver.

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Sam Ravnborg <sam@ravnborg.org>
Reviewed-by: Daniel Thompson <daniel.thompson@linaro.org>
Reviewed-by: Dan Carpenter <dan.carpenter@linaro.org>
Link: https://lore.kernel.org/r/20240319093915.31778-3-tzimmermann@suse.de
Signed-off-by: Lee Jones <lee@kernel.org>