usb: gadget: audio: convert to new interface of f_uac2

Use the new interface so that the old one can be removed.

Tested-by: Sebastian Reimers <sebastian.reimers@googlemail.com>
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 aa376f0..172a6a3 100644
--- a/drivers/usb/gadget/legacy/Kconfig
+++ b/drivers/usb/gadget/legacy/Kconfig
@@ -54,6 +54,7 @@
 	depends on SND
 	select USB_LIBCOMPOSITE
 	select SND_PCM
+	select USB_F_UAC2 if !GADGET_UAC1
 	help
 	  This Gadget Audio driver is compatible with USB Audio Class
 	  specification 2.0. It implements 1 AudioControl interface,