usb: xhci: Clear XHCI_STATE_DYING on start

For whatever reason if XHCI died in the previous instant
then it will never recover on the next xhci_start unless we
clear the DYING flag.

Cc: <stable@vger.kernel.org>
Signed-off-by: Roger Quadros <rogerq@ti.com>
Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>