media: ddbridge, cxd2099: include guard, fix unneeded NULL init, strings

Three really tiny minors in this single commit which all on their own
would just clutter up the commit history unnecessarily:

* ddbridge-regs.h is lacking an include guard. Add it.
* Fix an unnecessary NULL initialisation in ddbridge-ci. The declaration
  of the ci struct ptr is immediately followed by kzalloc().
* Clarify that the CXD2099AR is a Sony device in the cxd2099 driver at a
  few places including Kconfig.

Signed-off-by: Daniel Scheller <d.scheller@gmx.net>
Acked-by: Jasmin Jessich <jasmin@anw.at>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>