media: uapi: h264: Further clarify scaling lists order

Commit 0b0393d5 ("media: uapi: h264: clarify
expected scaling_list_4x4/8x8 order") improved the
documentation on H264 scaling lists order.

This commit improves the documentation by clarifying
that the lists themselves are expected in raster scan order.

Signed-off-by: Ezequiel Garcia <ezequiel@collabora.com>
Tested-by: Jonas Karlman <jonas@kwiboo.se>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>