USB: XHCI: fix memory leak of URB-private data

This patch (as1640) fixes a memory leak in xhci-hcd.  The urb_priv
data structure isn't always deallocated in the handle_tx_event()
routine for non-control transfers.  The patch adds a kfree() call so
that all paths end up freeing the memory properly.

This patch should be backported to kernels as old as 2.6.36, that
contain the commit 8e51adccd4c4b9ffcd509d7f2afce0a906139f75 "USB: xHCI:
Introduce urb_priv structure"

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com>
Reported-and-tested-by: Martin Mokrejs <mmokrejs@fold.natur.cuni.cz>
CC: <stable@vger.kernel.org>

drivers/usb/host/xhci-ring.c

@@ -2589,6 +2589,8 @@ cleanup:
 				(trb_comp_code != COMP_STALL &&
 					trb_comp_code != COMP_BABBLE))
 				xhci_urb_free_priv(xhci, urb_priv);
+			else
+				kfree(urb_priv);
 
 			usb_hcd_unlink_urb_from_ep(bus_to_hcd(urb->dev->bus), urb);
 			if ((urb->actual_length != urb->transfer_buffer_length &&