net: defxx: constify eisa_device_id

eisa_device_id are not supposed to change at runtime. All functions
working with eisa_device_id provided by <linux/eisa.h> work with
const eisa_device_id. So mark the non-const structs as const.

Signed-off-by: Arvind Yadav <arvind.yadav.cs@gmail.com>
Reviewed-by: Maciej W. Rozycki <macro@linux-mips.org>
Signed-off-by: David S. Miller <davem@davemloft.net>