[media] uvcvideo: Don't record timespec_sub

The statistics function subtracts two timespecs manually. A helper is
provided by the kernel to do this.

Replace the implementation, using the helper.
Signed-off-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>

drivers/media/usb/uvc/uvc_video.c

@@ -868,14 +868,8 @@ size_t uvc_video_stats_dump(struct uvc_streaming *stream, char *buf,
 	struct timespec ts;
 	size_t count = 0;
 
-	ts.tv_sec = stream->stats.stream.stop_ts.tv_sec
-		  - stream->stats.stream.start_ts.tv_sec;
-	ts.tv_nsec = stream->stats.stream.stop_ts.tv_nsec
-		   - stream->stats.stream.start_ts.tv_nsec;
-	if (ts.tv_nsec < 0) {
-		ts.tv_sec--;
-		ts.tv_nsec += 1000000000;
-	}
+	ts = timespec_sub(stream->stats.stream.stop_ts,
+			  stream->stats.stream.start_ts);
 
 	/* Compute the SCR.SOF frequency estimate. At the nominal 1kHz SOF
 	 * frequency this will not overflow before more than 1h.