drivers/net/eepro100.c: Fix compile warning

Fix this:
eepro100.c: In function 'eepro100_initialize':
eepro100.c:464:13: warning: assignment from incompatible pointer type
eepro100.c: In function 'eepro100_recv':
eepro100.c:694:4: warning: passing argument 1 of 'NetReceive' discards qualifiers from pointer target type
include/net.h:438:13: note: expected 'uchar *' but argument is of type 'volatile u8 *'

The use of a descriptor like this may mean DMA will update this at will
Beware this may be a source of trouble on some boards

Signed-off-by: Joe Hershberger <joe.hershberger@ni.com>
Cc: Joe Hershberger <joe.hershberger@gmail.com>