usb: gadget: FunctionFS: convert to new function interface with backward compatibility

This is required in order to integrate configfs support.
f_fs needs to be a separately compiled module and so it needs to use the new
interface.

Signed-off-by: Andrzej Pietrasiewicz <andrzej.p@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>

drivers/usb/gadget/g_ffs.c

@@ -54,6 +54,7 @@ static struct usb_function *f_rndis;
 #  endif
 #endif
 
+#define USB_FFS_INCLUDED
 #include "f_fs.c"
 
 #define DRIVER_NAME	"g_ffs"