usb: xhci: stop everything on the first call to xhci_stop

xhci_stop will be called twice, once for the shared hcd
and again for the primary hcd.

We stop the XHCI controller in any case so clean up
everything on the first call else we can timeout
waiting for pending requests to complete.

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>