V4L/DVB (9093): gspca: Cleanup code and small changes.

- convert some #define to enum.
- remove some comments.
- return ENOMEM on memory allocation failure.

Signed-off-by: Erik Andren <erik.andren@gmail.com>
Signed-off-by: Jean-Francois Moine <moinejf@free.fr>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>