[media] DocBook/audio.xml: Remove generic errors

Remove generic errors from ioctl() descriptions. For other ioctl's,
there's no generic section. So, just keep whatever is there.
Also remove the EINTERNAL error code, as no DVB driver returns
it, and this error code is not defined on POSIX or on Linux.

Acked-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>