xhci: gracefully handle xhci_irq dead device

commit 948fa135 upstream.

If the xHCI host controller has died (ie, device removed) or suffered
other serious fatal error (STS_FATAL), then xhci_irq should handle this
condition with IRQ_HANDLED instead of -ESHUTDOWN.

Signed-off-by: Joe Lawrence <joe.lawrence@stratus.com>
Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>