[media] em28xx: use usb_interface for dev_foo() calls

The usb_device->dev is not the right device for dev_foo() calls.
Instead, it should use usb_interface->dev.

Tested-by: Antti Palosaari <crope@iki.fi>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>