s390/qeth: constify attribute_group structures.

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

File size before:
   text	   data	    bss	    dec	    hex	filename
   6763	   1216	      0	   7979	   1f2b	drivers/s390/net/qeth_l3_sys.o

File size After adding 'const':
   text	   data	    bss	    dec	    hex	filename
   7019	    960	      0	   7971	   1f2b	drivers/s390/net/qeth_l3_sys.o
Signed-off-by: Arvind Yadav <arvind.yadav.cs@gmail.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

drivers/s390/net/qeth_l3_sys.c

@@ -350,7 +350,7 @@ static struct attribute *qeth_l3_device_attrs[] = {
 	NULL,
 };
 
-static struct attribute_group qeth_l3_device_attr_group = {
+static const struct attribute_group qeth_l3_device_attr_group = {
 	.attrs = qeth_l3_device_attrs,
 };
 
@@ -680,7 +680,7 @@ static struct attribute *qeth_ipato_device_attrs[] = {
 	NULL,
 };
 
-static struct attribute_group qeth_device_ipato_group = {
+static const struct attribute_group qeth_device_ipato_group = {
 	.name = "ipa_takeover",
 	.attrs = qeth_ipato_device_attrs,
 };
@@ -843,7 +843,7 @@ static struct attribute *qeth_vipa_device_attrs[] = {
 	NULL,
 };
 
-static struct attribute_group qeth_device_vipa_group = {
+static const struct attribute_group qeth_device_vipa_group = {
 	.name = "vipa",
 	.attrs = qeth_vipa_device_attrs,
 };
@@ -1006,7 +1006,7 @@ static struct attribute *qeth_rxip_device_attrs[] = {
 	NULL,
 };
 
-static struct attribute_group qeth_device_rxip_group = {
+static const struct attribute_group qeth_device_rxip_group = {
 	.name = "rxip",
 	.attrs = qeth_rxip_device_attrs,
 };