USB: xhci: Fail gracefully if there's no SS ep companion descriptor.

This is a work around for a bug in the SuperSpeed Endpoint Companion Descriptor
parsing code.  It fails in some corner cases, which means ep->ss_ep_comp may be
NULL.
Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/usb/host/xhci-mem.c

@@ -496,7 +496,12 @@ int xhci_endpoint_init(struct xhci_hcd *xhci,
 		max_packet = ep->desc.wMaxPacketSize;
 		ep_ctx->ep_info2 |= MAX_PACKET(max_packet);
 		/* dig out max burst from ep companion desc */
-		max_packet = ep->ss_ep_comp->desc.bMaxBurst;
+		if (!ep->ss_ep_comp) {
+			xhci_warn(xhci, "WARN no SS endpoint companion descriptor.\n");
+			max_packet = 0;
+		} else {
+			max_packet = ep->ss_ep_comp->desc.bMaxBurst;
+		}
 		ep_ctx->ep_info2 |= MAX_BURST(max_packet);
 		break;
 	case USB_SPEED_HIGH: