[media] DocBook: Remove a warning at videobuf2-v4l2.h

There's no need to document to_foo() macros, and the macro is
badly documented anyway. That removes this warning:
	include/media/videobuf2-v4l2.h:43: warning: No description found for parameter 'vb'

While here, remove the parenthesis for container_of(). The
countainer_of() already have parenthesis inside it.
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>

include/media/videobuf2-v4l2.h

@@ -36,10 +36,10 @@ struct vb2_v4l2_buffer {
 	__u32			sequence;
 };
 
-/**
+/*
  * to_vb2_v4l2_buffer() - cast struct vb2_buffer * to struct vb2_v4l2_buffer *
  */
 #define to_vb2_v4l2_buffer(vb) \
-	(container_of(vb, struct vb2_v4l2_buffer, vb2_buf))
+	container_of(vb, struct vb2_v4l2_buffer, vb2_buf)
 
 #endif /* _MEDIA_VIDEOBUF2_V4L2_H */