[media] cx23885: fix querycap

cap->device_caps wasn't set in cx23885-417.c causing a warning from
the v4l2-core.

Reported-by: Joseph Jasi <joe.yasi@gmail.com>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Cc: <stable@vger.kernel.org>      # for v3.19 and up
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>