usb: gadget: printer: convert to new interface of f_printer

The goal is to remove the old function interface, so its (only) user
must be converted to the new interface.

Signed-off-by: Andrzej Pietrasiewicz <andrzej.p@samsung.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>
diff --git a/drivers/usb/gadget/legacy/Kconfig b/drivers/usb/gadget/legacy/Kconfig
index 113c87e..d5a7102 100644
--- a/drivers/usb/gadget/legacy/Kconfig
+++ b/drivers/usb/gadget/legacy/Kconfig
@@ -301,6 +301,7 @@
 config USB_G_PRINTER
 	tristate "Printer Gadget"
 	select USB_LIBCOMPOSITE
+	select USB_F_PRINTER
 	help
 	  The Printer Gadget channels data between the USB host and a
 	  userspace program driving the print engine. The user space