staging: unisys: make visorbus_dev_groups static

visorbus_dev_groups is not referenced outside visorbus_main.c, so it can
be declared static.

Found using sparse.
Signed-off-by: Michał Kępień <kernel@kempniu.pl>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/unisys/visorbus/visorbus_main.c

@@ -96,7 +96,7 @@ static const struct attribute_group visorbus_dev_group = {
 	.attrs = visorbus_dev_attrs,
 };
 
-const struct attribute_group *visorbus_dev_groups[] = {
+static const struct attribute_group *visorbus_dev_groups[] = {
 	&visorbus_dev_group,
 	NULL,
 };