xhci: xhci-mem: off by one in xhci_stream_id_to_ring()

The > should be >= here so that we don't read one element beyond the end
of the ep->stream_info->stream_rings[] array.

Fixes: e9df17eb ("USB: xhci: Correct assumptions about number of rings per endpoint.")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>