usb: gadget: Compilation warning fix

A compilation warning was added by the patch
"usb: gadget: use config_ep_by_speed() instead of ep_choose()".
This patch fixed it.

Signed-off-by: Tatyana Brokhman <tlinder@codeaurora.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
diff --git a/drivers/usb/gadget/storage_common.c b/drivers/usb/gadget/storage_common.c
index 1fa4f70..d3dd227 100644
--- a/drivers/usb/gadget/storage_common.c
+++ b/drivers/usb/gadget/storage_common.c
@@ -494,7 +494,7 @@
 };
 
 /* Maxpacket and other transfer characteristics vary by speed. */
-static struct usb_endpoint_descriptor *
+static __maybe_unused struct usb_endpoint_descriptor *
 fsg_ep_desc(struct usb_gadget *g, struct usb_endpoint_descriptor *fs,
 		struct usb_endpoint_descriptor *hs)
 {