greybus: interface: declare gb_interface_destroy()

Add a public declaration for gb_interface_destroy(), matching
gb_interface_create().

It's not yet used outside "interface.c" but I suppose it
could be, and its scope is currently public.
Signed-off-by: Alex Elder <elder@linaro.org>
Reviewed-by: Bryan O'Donoghue <bryan.odonoghue@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>

drivers/staging/greybus/interface.h

@@ -51,6 +51,7 @@ struct gb_interface *gb_interface_find(struct greybus_host_device *hd,
 
 struct gb_interface *gb_interface_create(struct greybus_host_device *hd,
 					 u8 interface_id);
+void gb_interface_destroy(struct gb_interface *intf);
 int gb_interface_init(struct gb_interface *intf, u8 device_id);
 void gb_interface_remove(struct greybus_host_device *hd, u8 interface_id);
 void gb_interfaces_remove(struct greybus_host_device *hd);