chelsio: use const for virtual functions

There are several uses of _ops structure in this driver that
can be converted to const.

Signed-off-by: Stephen Hemminger <shemminger@linux-foundation.org>
Signed-off-by: Jeff Garzik <jeff@garzik.org>
diff --git a/drivers/net/chelsio/mac.c b/drivers/net/chelsio/mac.c
index 6af39dc..1d97282 100644
--- a/drivers/net/chelsio/mac.c
+++ b/drivers/net/chelsio/mac.c
@@ -363,6 +363,6 @@
 	return mac;
 }
 
-struct gmac t1_chelsio_mac_ops = {
+const struct gmac t1_chelsio_mac_ops = {
 	.create = mac_create
 };