This patch fixes throttling problems in the ftdi_sio driver for the
2.6 kernel.  The old throttling mechanism (unlinking the read urb)
often failed to work, and even it did work, would lose any data
held in the transfer buffer.  The new mechanism presented here is
based on what the whitehead driver does (defer processing and
resubmitting of the read urb until unthrottled).
Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <greg@kroah.com>