[media] dib0700: fix possible NULL pointer dereference

Seems like 'adap->fe' test for NULL was meant to be before we dereference
that pointer.

Signed-off-by: Mariusz Kozlowski <mk@lab.zgora.pl>
Acked-by: Patrick Boettcher <patrick.boettcher@dibcom.fr>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>