net: dm9000x: use standard I/O accessors

The current dm9000x driver accesses its memory mapped registers directly
instead of using the standard I/O accessors.  This can cause problems on
Blackfin systems as the accesses can get out of order.  So convert the
direct volatile dereferences to use the normal in/out macros.

Signed-off-by: Mike Frysinger <vapier@gentoo.org>
Signed-off-by: Ben Warren <biggerbadderben@gmail.com>