USB: composite: Fix bug: should test set_alt function pointer before use it

Signed-off-by: Bryan Wu <cooloney@kernel.org>
Acked-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/usb/gadget/composite.c

@@ -772,7 +772,7 @@ composite_setup(struct usb_gadget *gadget, const struct usb_ctrlrequest *ctrl)
 		f = cdev->config->interface[w_index];
 		if (!f)
 			break;
-		if (w_value && !f->get_alt)
+		if (w_value && !f->set_alt)
 			break;
 		value = f->set_alt(f, w_index, w_value);
 		break;