xhci: Don't show incorrect WARN message about events for empty rings

xHC can generate two events for a short transfer if the short TRB and
last TRB in the TD are not the same TRB.

The driver will handle the TD after the first short event, and remove
it from its internal list. Driver then incorrectly prints a warning
for the second event:

"WARN Event TRB for slot x ep y with no TDs queued"

Fix this by not printing a warning if we get a event on a empty list
if the previous event was a short event.

Cc: <stable@vger.kernel.org>
Signed-off-by: NMathias Nyman <mathias.nyman@linux.intel.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/host/xhci-ring.c

@@ -2477,12 +2477,16 @@ static int handle_tx_event(struct xhci_hcd *xhci,
 		 */
 		if (list_empty(&ep_ring->td_list)) {
 			/*
-			 * A stopped endpoint may generate an extra completion
-			 * event if the device was suspended.  Don't print
-			 * warnings.
+			 * Don't print wanings if it's due to a stopped endpoint
+			 * generating an extra completion event if the device
+			 * was suspended. Or, a event for the last TRB of a
+			 * short TD we already got a short event for.
+			 * The short TD is already removed from the TD list.
 			 */
+
 			if (!(trb_comp_code == COMP_STOPPED ||
-				trb_comp_code == COMP_STOPPED_LENGTH_INVALID)) {
+			      trb_comp_code == COMP_STOPPED_LENGTH_INVALID ||
+			      ep_ring->last_td_was_short)) {
 				xhci_warn(xhci, "WARN Event TRB for slot %d ep %d with no TDs queued?\n",
 						TRB_TO_SLOT_ID(le32_to_cpu(event->flags)),
 						ep_index);