[media] cx231xx: remove useless 'lif' variable in cx231xx_usb_probe()

Now that we set the intfdata on the right interface, the 'lif'
variable is useless.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>