media: videobuf2: Exit promptly if size = 0

Exit as soon as possible if a driver wants to allocate a buffer of
size 0, and print a warning to help fixing the issue.
Signed-off-by: Ricardo Ribalda <ribalda@chromium.org>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>

drivers/media/common/videobuf2/videobuf2-dma-sg.c

@@ -105,7 +105,7 @@ static void *vb2_dma_sg_alloc(struct device *dev, unsigned long dma_attrs,
 	int ret;
 	int num_pages;
 
-	if (WARN_ON(!dev))
+	if (WARN_ON(!dev) || WARN_ON(!size))
 		return ERR_PTR(-EINVAL);
 
 	buf = kzalloc(sizeof *buf, GFP_KERNEL);