driver model: constify attribute groups

Let attribute group vectors be declared "const".  We'd
like to let most attribute metadata live in read-only
sections... this is a start.

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

diff --git a/drivers/s390/cio/css.c b/drivers/s390/cio/css.c
index e995123..393c73c 100644
--- a/drivers/s390/cio/css.c
+++ b/drivers/s390/cio/css.c
@@ -266,7 +266,7 @@
 	.attrs = subch_attrs,
 };
 
-static struct attribute_group *default_subch_attr_groups[] = {
+static const struct attribute_group *default_subch_attr_groups[] = {
 	&subch_attr_group,
 	NULL,
 };