xhci: don't try to reset the host if it is unaccessible

There is no point in trying to reset the host controller by writing
to its registers if host is removed and registers just return 0xffffffff

bail out and return -ENODEV instead

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