backlight: ili922x: Remove invalid use of kerneldoc syntax

Kerneldoc is for documenting function arguments and return values.

Prevents warnings like:

 drivers/video/backlight/ili922x.c:127: warning: cannot understand function prototype: 'int ili922x_id = 1; '
 drivers/video/backlight/ili922x.c:136: warning: cannot understand function prototype: 'struct ili922x '

Cc: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Cc: Software Engineering <sbabic@denx.de>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Reviewed-by: Daniel Thompson <daniel.thompson@linaro.org>
Reviewed-by: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>