xhci: Fix null pointer dereference if xhci initialization fails

If xhci initialization fails before the roothub bandwidth
domains (xhci->rh_bw[i]) are allocated it will oops when
trying to access rh_bw members in xhci_mem_cleanup().

Reported-by: Manuel Reimer <manuel.reimer@gmx.de>
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/host/xhci-mem.c

@@ -1819,7 +1819,7 @@ void xhci_mem_cleanup(struct xhci_hcd *xhci)
 	xhci_cleanup_command_queue(xhci);
 
 	num_ports = HCS_MAX_PORTS(xhci->hcs_params1);
-	for (i = 0; i < num_ports; i++) {
+	for (i = 0; i < num_ports && xhci->rh_bw; i++) {
 		struct xhci_interval_bw_table *bwt = &xhci->rh_bw[i].bw_table;
 		for (j = 0; j < XHCI_MAX_INTERVAL; j++) {
 			struct list_head *ep = &bwt->interval_bw[j].endpoints;