[media] tm6000: Don't try to use a non-existing interface

> [34883.426065] tm6000 #0: registered device video0
> [34883.430591] Trident TVMaster TM5600/TM6000/TM6010 USB2 board (Load status: 0)
> [34883.437763] usbcore: registered new interface driver tm6000
> [34884.608372] BUG: unable to handle kernel NULL pointer dereference at 00000002
> [34884.615514] IP: [<f8c4ceea>] tm6000_reset+0xd7/0x11c [tm6000]

The dev->int_in USB interfaces is used by some devices for the
Remote Controller. Not all devices seem to define this interface,
so, tm6000_reset should not try to set the interface to it on
such devices.

Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>