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>

block/genhd.c

@@ -903,7 +903,7 @@ static struct attribute_group disk_attr_group = {
 	.attrs = disk_attrs,
 };
 
-static struct attribute_group *disk_attr_groups[] = {
+static const struct attribute_group *disk_attr_groups[] = {
 	&disk_attr_group,
 	NULL
 };