usb: xhci: fix wild pointers in xhci_mem_cleanup

commit 71504062 upstream.

This patch fixes some wild pointers produced by xhci_mem_cleanup.
These wild pointers will cause system crash if xhci_mem_cleanup()
is called twice.
Reported-and-tested-by: Pengcheng Li <lpc.li@hisilicon.com>
Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
[bwh: Backported to 3.2: there's no xhci_hcd::ext_caps field to clear]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

drivers/usb/host/xhci-mem.c

@@ -1789,6 +1789,11 @@ void xhci_mem_cleanup(struct xhci_hcd *xhci)
 	kfree(xhci->port_array);
 	kfree(xhci->rh_bw);
 
+	xhci->usb2_ports = NULL;
+	xhci->usb3_ports = NULL;
+	xhci->port_array = NULL;
+	xhci->rh_bw = NULL;
+
 	xhci->page_size = 0;
 	xhci->page_shift = 0;
 	xhci->bus_state[0].bus_suspended = 0;