usbnet cdc_subset: fix issues talking to PXA gadgets

The host-side CDC subset driver is binding more specifically
than it should ... only to PXA 210/25x/26x Linux-USB gadgets.

Loosen that restriction to match the gadget driver driver.
This will various PXA 27x and PXA 3xx devices happier when
talking to Linux hosts, potentially others.

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Tested-by: Aric D. Blumer <aric@sdgsystems.com>
Signed-off-by: David S. Miller <davem@davemloft.net>