media: ddbridge/ci: further deduplicate code/logic in ddb_ci_attach()

Deduplicate the checks for a valid ptr in port->en, and also handle the
default case to also catch eventually yet unsupported CI hardware.

Signed-off-by: Daniel Scheller <d.scheller@gmx.net>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>