V4L/DVB: au0828: move dereference below sanity checks

This function has sanity checks to make sure that "dev" is non-null.  I
moved the dereference down below the checks.  In the current code "dev"
is never actually null.

Signed-off-by: Dan Carpenter <error27@gmail.com>
Acked-by: Devin Heitmueller <dheitmueller@kernellabs.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>