[media] uvcvideo: Fix alternate setting selection

The alternate setting number is not equal to the alternate setting index
in the interface alternate settings table. Use the alternate setting
number from the interface descriptor when calling usb_set_interface().

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Ming Lei <ming.lei@canonical.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>