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/usb/core/endpoint.c b/drivers/usb/core/endpoint.c
index bc39fc4..fdfaa78 100644
--- a/drivers/usb/core/endpoint.c
+++ b/drivers/usb/core/endpoint.c
@@ -154,7 +154,7 @@
 static struct attribute_group ep_dev_attr_grp = {
 	.attrs = ep_dev_attrs,
 };
-static struct attribute_group *ep_dev_groups[] = {
+static const struct attribute_group *ep_dev_groups[] = {
 	&ep_dev_attr_grp,
 	NULL
 };