staging: xillybus: Changed Open Firmware "compatible" property

The previous "compatible" string was poorly chosen, but remains in the
match list to support existing DTBs. There is no risk for a naming clash.

Signed-off-by: Eli Billauer <eli.billauer@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>