media: saa7134: improve f->fmt.win.clips NULL check

Fix this smatch error:

saa7134-video.c:1286 saa7134_g_fmt_vid_overlay() error: we previously assumed 'f->fmt.win.clips' could be null (see line 1279)

This is actually a false error since if f->fmt.win.clips is NULL, clipcount
will be set to 0, so the clips array won't be touched, but it doesn't hurt
to make this explicit in the code.
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>

drivers/media/pci/saa7134/saa7134-video.c

@@ -1276,8 +1276,10 @@ static int saa7134_g_fmt_vid_overlay(struct file *file, void *priv,
 		return -EINVAL;
 	}
 	f->fmt.win = dev->win;
-	if (!f->fmt.win.clips)
-		clipcount = 0;
+	if (!f->fmt.win.clips) {
+		f->fmt.win.clipcount = 0;
+		return 0;
+	}
 	if (dev->nclips < clipcount)
 		clipcount = dev->nclips;
 	f->fmt.win.clipcount = clipcount;