[media] bttv: fix missing irq after reloading driver

If pci_disable_device() isn't called when the driver is removed, then
the next time when it is loaded the irq isn't found.

I'm pretty sure this used to work in the past, but calling
pci_disable_device() is clearly the correct method and this makes
it work again.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>