staging: fbtft: Remove reference to fb_blank

The field fb_blank in struct backlight_properties is deprecated and
should not be used. Don't output its value in the driver's debug print.

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Dan Carpenter <dan.carpenter@linaro.org>
Link: https://lore.kernel.org/r/20240319093915.31778-6-tzimmermann@suse.de


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