net: dm9k: Fix resource sizes in add_dm9000_device
The dm9000 needs a resource for an index register and one for
the data register. Both should have a size of the access width,
and not two times the access width. The current code is probably
a leftover when the dm9000 had only one resource.
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>