vfio/mdev: add static modifier to add_mdev_supported_type

Set add_mdev_supported_type as static since it is only used within
mdev_sysfs.c.  This fixes -Wmissing-prototypes gcc warning.
Signed-off-by: Paolo Cretaro <paolocretaro@gmail.com>
Reviewed-by: Cornelia Huck <cohuck@redhat.com>
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>

drivers/vfio/mdev/mdev_sysfs.c

@@ -92,8 +92,8 @@ static struct kobj_type mdev_type_ktype = {
 	.release = mdev_type_release,
 };
 
-struct mdev_type *add_mdev_supported_type(struct mdev_parent *parent,
-					  struct attribute_group *group)
+static struct mdev_type *add_mdev_supported_type(struct mdev_parent *parent,
+						 struct attribute_group *group)
 {
 	struct mdev_type *type;
 	int ret;