media: saa7146: Avoid using BUG_ON as an assertion

In video_begin and video_end, saa7146_format_by_fourcc can return
NULL and is checked via BUG_ON. However, by returning the error
to the callers upstream, we can avoid the crash and handle it via
recovery code.
Signed-off-by: Aditya Pakki <pakki001@umn.edu>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>

drivers/media/common/saa7146/saa7146_video.c

@@ -345,7 +345,8 @@ static int video_begin(struct saa7146_fh *fh)
 
 	fmt = saa7146_format_by_fourcc(dev, vv->video_fmt.pixelformat);
 	/* we need to have a valid format set here */
-	BUG_ON(NULL == fmt);
+	if (!fmt)
+		return -EINVAL;
 
 	if (0 != (fmt->flags & FORMAT_IS_PLANAR)) {
 		resource = RESOURCE_DMA1_HPS|RESOURCE_DMA2_CLP|RESOURCE_DMA3_BRS;
@@ -398,7 +399,8 @@ static int video_end(struct saa7146_fh *fh, struct file *file)
 
 	fmt = saa7146_format_by_fourcc(dev, vv->video_fmt.pixelformat);
 	/* we need to have a valid format set here */
-	BUG_ON(NULL == fmt);
+	if (!fmt)
+		return -EINVAL;
 
 	if (0 != (fmt->flags & FORMAT_IS_PLANAR)) {
 		resource = RESOURCE_DMA1_HPS|RESOURCE_DMA2_CLP|RESOURCE_DMA3_BRS;