First, determine the source file for this particular driver.
Found it at drivers/usb/serial/ftdi_sio.c
.
./scripts/get_maintainer.pl drivers/usb/serial/ftdi_sio.c
And the results:
Johan Hovold <johan@kernel.org> (maintainer:USB SERIAL SUBSYSTEM)
Greg Kroah-Hartman <gregkh@linuxfoundation.org> (supporter:USB SUBSYSTEM)
linux-usb@vger.kernel.org (open list:USB SERIAL SUBSYSTEM)
linux-kernel@vger.kernel.org (open list)
Now we know who to ping for help with this particular driver, and which e-mail addresses should be CC'ed when submitting a patch against this driver.