staging: line6: Filter on UX2 interfaces

The driver only supports interface 0 of the TonePort UX2 and POD Studio
UX2 devices.  Use the device table to filter on this.

Signed-off-by: Chris Rorvick <chris@rorvick.com>
Reviewed-by: Stefan Hajnoczi <stefanha@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>