drivers/net/cs8900.c: Fix compile warning

Fix this:
cs8900.c: In function 'cs8900_initialize':
cs8900.c:326:12: warning: assignment from incompatible pointer type

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