media: uvcvideo: Avoid returning invalid controls

If the memory where ctrl_found is placed has the value of uvc_ctrl and
__uvc_find_control does not find the control we will return an invalid
index.

Fixes: 6350d6a4 ("media: uvcvideo: Set error_idx during ctrl_commit errors")
Signed-off-by: Ricardo Ribalda <ribalda@chromium.org>
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>

drivers/media/usb/uvc/uvc_ctrl.c

@@ -1639,7 +1639,7 @@ static int uvc_ctrl_find_ctrl_idx(struct uvc_entity *entity,
 				  struct uvc_control *uvc_control)
 {
 	struct uvc_control_mapping *mapping = NULL;
-	struct uvc_control *ctrl_found;
+	struct uvc_control *ctrl_found = NULL;
 	unsigned int i;
 
 	if (!entity)