rm9200 ethernet driver: board-specific quirk (csb337)

CSB337 boards originally shipped with MicroMonitor, not U-Boot;
and with a version using a different convention for recording
Ethernet addresses than anyone else.  To avoid breaking Linux
when it uses U-Boot, have it use the same convention on that
hardware.

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Ben Warren <biggerbadderben@gmail.com>