video: rockchip: mpp: when meet unknown cmd, not return error.

reason: when kernel version later than mpp which user space, then
it will meet unknow cmd. however, it should not return error, and
let it continue instead.

Change-Id: I1209c27ef8de98f25b47700bc48dfcff305e0c0e
Signed-off-by: Ding Wei <leo.ding@rock-chips.com>

drivers/video/rockchip/mpp/mpp_common.c

@@ -1110,7 +1110,6 @@ static int mpp_process_request(struct mpp_session *session,
 			return mpp->dev_ops->ioctl(session, req);
 
 		mpp_debug(DEBUG_IOCTL, "unknown mpp ioctl cmd %x\n", req->cmd);
-		return -ENOIOCTLCMD;
 	} break;
 	}