usb: gadget: f_uac2: fix bFirstInterface in composite gadget

BugLink: https://bugs.launchpad.net/bugs/1775771

[ Upstream commit 8813a59e ]

If there are multiple functions associated with a configuration, then
the UAC2 interfaces may not start at zero.  Set the correct first
interface number in the association descriptor so that the audio
interfaces are enumerated correctly in this case.
Reviewed-by: Krzysztof Opasiak <k.opasiak@samsung.com>
Signed-off-by: John Keeping <john@metanate.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Juerg Haefliger <juergh@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>

drivers/usb/gadget/function/f_uac2.c

@@ -1052,6 +1052,8 @@ afunc_bind(struct usb_configuration *cfg, struct usb_function *fn)
 		dev_err(dev, "%s:%d Error!\n", __func__, __LINE__);
 		return ret;
 	}
+	iad_desc.bFirstInterface = ret;
+
 	std_ac_if_desc.bInterfaceNumber = ret;
 	agdev->ac_intf = ret;
 	agdev->ac_alt = 0;