net/s390 drivers: add missing 'const' attribute

Add missing 'const' attribute to avoid the following compile warnings:

drivers/s390/net/ctcm_main.c: In function 'ctcm_init':
drivers/s390/net/ctcm_main.c:1864: warning: assignment from incompatible pointer type
drivers/s390/net/lcs.c: In function 'lcs_init_module':
drivers/s390/net/lcs.c:2468: warning: assignment from incompatible pointer type
drivers/s390/net/claw.c: In function 'claw_init':
drivers/s390/net/claw.c:3408: warning: assignment from incompatible pointer type

Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/drivers/s390/net/claw.c b/drivers/s390/net/claw.c
index cf283e3..3c77bfe 100644
--- a/drivers/s390/net/claw.c
+++ b/drivers/s390/net/claw.c
@@ -310,7 +310,7 @@
 	.attrs = claw_group_attrs,
 };
 
-static struct attribute_group *claw_group_attr_groups[] = {
+static const struct attribute_group *claw_group_attr_groups[] = {
 	&claw_group_attr_group,
 	NULL,
 };