net: dm9000x: re-add casts to I/O pointers to fix gcc warnings

net: dm9000x: re-add casts to I/O pointers to fix gcc warnings

The DM9000 in/out helper functions were casting the register address when
it was accessing things directly (pre commit a45dde2293c816138e53c).  But
when it was changed to using the in/out helpers, those casts were dropped
because those functions don't take pointers.  Even more recently, those
functions were then changed to use the read/write helpers, but the casts
were not re-added.  This is necessary because the read/write helpers do
take pointers.  Otherwise we get a lot of warnings like:
dm9000x.c: In function 'dm9000_inblk_8bit':
dm9000x.c:172: warning: passing argument 1 of 'readb'
	makes pointer from integer without a cast

Signed-off-by: Mike Frysinger <vapier@gentoo.org>
Tested-by: Thomas Weber <weber@corscience.de>
Signed-off-by: Ben Warren <biggerbadderben@gmail.com>