[media] v4l: vs6624: Fix warning due to unused function

vs6624_read() is only called in the conditionally-compiled
vs6624_g_register() function. Make the former conditionally-compiled as
well to silence build warnings.
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Acked-by: Scott Jiang <scott.jiang.linux@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>

drivers/media/i2c/vs6624.c

@@ -503,6 +503,7 @@ static inline struct v4l2_subdev *to_sd(struct v4l2_ctrl *ctrl)
 	return &container_of(ctrl->handler, struct vs6624, hdl)->sd;
 }
 
+#ifdef CONFIG_VIDEO_ADV_DEBUG
 static int vs6624_read(struct v4l2_subdev *sd, u16 index)
 {
 	struct i2c_client *client = v4l2_get_subdevdata(sd);
@@ -515,6 +516,7 @@ static int vs6624_read(struct v4l2_subdev *sd, u16 index)
 
 	return buf[0];
 }
+#endif
 
 static int vs6624_write(struct v4l2_subdev *sd, u16 index,
 				u8 value)