[media] tlg2300: fix missing check for audio creation

If we fail to set up the capture device we go through negative indexes and
badness happens. Add the missing test.
Resolves-bug: https://bugzilla.kernel.org/show_bug.cgi?id=44551

Signed-off-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>