[media] cx18: fix kernel oops with tda8290 tuner

This was caused by an uninitialized setup.config field.

Based on a suggestion from Devin Heitmueller.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Thanks-to: Devin Heitmueller <dheitmueller@kernellabs.com>
Reported-by: Scott Robinson <scott.robinson55@gmail.com>
Tested-by: Hans Verkuil <hans.verkuil@cisco.com>
Cc: stable@vger.kernel.org      # for v3.10 and up
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>