backlight: lcd: Add missing kerneldoc entry for 'struct device parent'

This has been missing since the conversion to 'struct device' in 2007.

Cc: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Cc: Jamey Hicks <jamey.hicks@hp.com>
Cc: Andrew Zabolotny <zap@homelink.ru>
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>

drivers/video/backlight/lcd.c

@@ -179,6 +179,7 @@ ATTRIBUTE_GROUPS(lcd_device);
  * lcd_device_register - register a new object of lcd_device class.
  * @name: the name of the new object(must be the same as the name of the
  *   respective framebuffer device).
+ * @parent: pointer to the parent's struct device .
  * @devdata: an optional pointer to be stored in the device. The
  *   methods may retrieve it by using lcd_get_data(ld).
  * @ops: the lcd operations structure.