USB: serial: xr: claim both interfaces

Use the new multi-interface support in USB serial core to properly claim
also the control interface during probe. This prevents having another
driver claim the control interface and makes core allocate resources
also for the interrupt endpoint (currently unused).

Switch to probing only Communication Class interfaces and use the Union
functional descriptor to determine the corresponding data interface.

Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Johan Hovold <johan@kernel.org>