s390/cio: 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.
Signed-off-by: Arvind Yadav <arvind.yadav.cs@gmail.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

drivers/s390/cio/device.c

@@ -612,7 +612,7 @@ static struct attribute *io_subchannel_attrs[] = {
 	NULL,
 };
 
-static struct attribute_group io_subchannel_attr_group = {
+static const struct attribute_group io_subchannel_attr_group = {
 	.attrs = io_subchannel_attrs,
 };
 
@@ -626,7 +626,7 @@ static struct attribute * ccwdev_attrs[] = {
 	NULL,
 };
 
-static struct attribute_group ccwdev_attr_group = {
+static const struct attribute_group ccwdev_attr_group = {
 	.attrs = ccwdev_attrs,
 };