[media] drivers: media: platform: vivid: Fix possible null derefrence

Check for dev_fmt being null before derefrencing it, to assign it
to planes.

Found using Coccinelle.
Signed-off-by: Tapasweni Pathak <tapaswenipathak@gmail.com>
Acked-by: Julia Lawall <julia.lawall@lip6.fr>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>

drivers/media/platform/vivid/vivid-vid-out.c

@@ -114,7 +114,7 @@ static int vid_out_buf_prepare(struct vb2_buffer *vb)
 {
 	struct vivid_dev *dev = vb2_get_drv_priv(vb->vb2_queue);
 	unsigned long size;
-	unsigned planes = dev->fmt_out->planes;
+	unsigned planes;
 	unsigned p;
 
 	dprintk(dev, 1, "%s\n", __func__);
@@ -122,6 +122,8 @@ static int vid_out_buf_prepare(struct vb2_buffer *vb)
 	if (WARN_ON(NULL == dev->fmt_out))
 		return -EINVAL;
 
+	planes = dev->fmt_out->planes;
+
 	if (dev->buf_prepare_error) {
 		/*
 		 * Error injection: test what happens if buf_prepare() returns