xhci: Fix NULL pointer deref in handle_port_status()

When we get a port status change event, we need to figure out what type of
port it came from: a USB 3.0 port, or a USB 2.0/1.1 port.  We can't know
which usb_hcd to use until that point, so hcd will be NULL for part of the
function.  Unfortunately, if any of the sanity checks fail, we'll jump to
the cleanup label before hcd is set to a valid pointer, and then we'll
attempt to tell the USB core to kick the hcd, which is NULL.

Skip kicking the roothub if the sanity checks fail.

Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com>