[media] media: vb2: fix allocation failure check

__vb2_queue_alloc function returns the number of successfully allocated
buffers. There is no point in checking if the returned value is negative.
If this function returns 0, videobuf2 should just return -ENOMEM to
userspace, because no driver can work without memory buffers.

Reported-by: Jonathan Corbet <corbet@lwn.net>
Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
CC: Pawel Osciak <pawel@osciak.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

drivers/media/video/videobuf2-core.c

@@ -532,9 +532,9 @@ int vb2_reqbufs(struct vb2_queue *q, struct v4l2_requestbuffers *req)
 	/* Finally, allocate buffers and video memory */
 	ret = __vb2_queue_alloc(q, req->memory, num_buffers, num_planes,
 				plane_sizes);
-	if (ret < 0) {
-		dprintk(1, "Memory allocation failed with error: %d\n", ret);
-		return ret;
+	if (ret == 0) {
+		dprintk(1, "Memory allocation failed\n");
+		return -ENOMEM;
 	}
 
 	/*