backlight: Remove obsolete comment for ->state

Jani spotted this when reviewing my earlier patch to remove the driver
internal usage of this field in:

  Commit 3cf91ad ("backlight: Nuke BL_CORE_DRIVER1")

Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Acked-by: Daniel Thompson <daniel.thompson@linaro.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>

include/linux/backlight.h

@@ -79,7 +79,6 @@ struct backlight_properties {
 	/* Backlight type */
 	enum backlight_type type;
 	/* Flags used to signal drivers of state changes */
-	/* Upper 4 bits are reserved for driver internal use */
 	unsigned int state;
 
 #define BL_CORE_SUSPENDED	(1 << 0)	/* backlight is suspended */