usb: gadget: udc: fsl: Add missing complete function.

Commit 304f7e5e1d08 ("usb: gadget: Refactor request completion")
removed check if req->req.complete is non-NULL, resulting in a NULL
pointer derefence and a kernel panic.
This patch adds an empty complete function instead of re-introducing
the req->req.complete check.

Fixes: 304f7e5e1d08 ("usb: gadget: Refactor request completion")

Signed-off-by: Magnus Lilja <lilja.magnus@gmail.com>
Cc: <stable@vger.kernel.org> # 3.18+
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>

drivers/usb/gadget/udc/fsl_udc_core.c

@@ -1248,6 +1248,12 @@ static const struct usb_gadget_ops fsl_gadget_ops = {
 	.udc_stop = fsl_udc_stop,
 };
 
+/*
+ * Empty complete function used by this driver to fill in the req->complete
+ * field when creating a request since the complete field is mandatory.
+ */
+static void fsl_noop_complete(struct usb_ep *ep, struct usb_request *req) { }
+
 /* Set protocol stall on ep0, protocol stall will automatically be cleared
    on new transaction */
 static void ep0stall(struct fsl_udc *udc)
@@ -1282,7 +1288,7 @@ static int ep0_prime_status(struct fsl_udc *udc, int direction)
 	req->req.length = 0;
 	req->req.status = -EINPROGRESS;
 	req->req.actual = 0;
-	req->req.complete = NULL;
+	req->req.complete = fsl_noop_complete;
 	req->dtd_count = 0;
 
 	ret = usb_gadget_map_request(&ep->udc->gadget, &req->req, ep_is_in(ep));
@@ -1365,7 +1371,7 @@ static void ch9getstatus(struct fsl_udc *udc, u8 request_type, u16 value,
 	req->req.length = 2;
 	req->req.status = -EINPROGRESS;
 	req->req.actual = 0;
-	req->req.complete = NULL;
+	req->req.complete = fsl_noop_complete;
 	req->dtd_count = 0;
 
 	ret = usb_gadget_map_request(&ep->udc->gadget, &req->req, ep_is_in(ep));