xhci: fix list access before init

If for whatever reason we fall into fail path in xhci_mem_init()
before bw table gets initialized we may access the uninitialized lists
in xhci_mem_cleanup().

Check for bw table before traversing lists in cleanup routine.

This patch should be backported to kernels as old as 3.2, that contain
the commit 839c817ce67178ca3c7c7ad534c571bba1e69ebe "xhci: Store
information about roothubs and TTs."

Reported-by: Sergey Dyasly <dserrg@gmail.com>
Tested-by: Sergey Dyasly <dserrg@gmail.com>
Signed-off-by: Vladimir Murzin <murzin.v@gmail.com>
Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com>
Cc: stable@vger.kernel.org

drivers/usb/host/xhci-mem.c

@@ -1827,6 +1827,9 @@ void xhci_mem_cleanup(struct xhci_hcd *xhci)
 	}
 	spin_unlock_irqrestore(&xhci->lock, flags);
 
+	if (!xhci->rh_bw)
+		goto no_bw;
+
 	num_ports = HCS_MAX_PORTS(xhci->hcs_params1);
 	for (i = 0; i < num_ports; i++) {
 		struct xhci_interval_bw_table *bwt = &xhci->rh_bw[i].bw_table;
@@ -1845,6 +1848,7 @@ void xhci_mem_cleanup(struct xhci_hcd *xhci)
 		}
 	}
 
+no_bw:
 	xhci->num_usb2_ports = 0;
 	xhci->num_usb3_ports = 0;
 	xhci->num_active_eps = 0;