usb: diag: Add NULL pointer check after ep_autoconfig

ep_autoconfig api can fail and return null endpoint. Add a
null pointer check after ep_auotconfig

Signed-off-by: Vamsi Krishna <vskrishn@codeaurora.org>
diff --git a/drivers/usb/gadget/f_diag.c b/drivers/usb/gadget/f_diag.c
index 0510547..e276be6 100644
--- a/drivers/usb/gadget/f_diag.c
+++ b/drivers/usb/gadget/f_diag.c
@@ -575,10 +575,14 @@
 	intf_desc.bInterfaceNumber =  usb_interface_id(c, f);
 
 	ep = usb_ep_autoconfig(cdev->gadget, &fs_bulk_in_desc);
+	if (!ep)
+		goto fail;
 	ctxt->in = ep;
 	ep->driver_data = ctxt;
 
 	ep = usb_ep_autoconfig(cdev->gadget, &fs_bulk_out_desc);
+	if (!ep)
+		goto fail;
 	ctxt->out = ep;
 	ep->driver_data = ctxt;