media: ddbridge: Remove useless license text when SPDX-License-Identifier is already used

An SPDX-License-Identifier is already in place. There is no need to
duplicate part of the corresponding license.

While at it, a few comments at the end of some .h files have been updated
to reflect the correct include guard name (missing '_' and co.)

Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>