staging: comedi: serial2002: rename all the static functions

Many of the static functions in this driver have names that could
potentially clash with external symbols (tty_ioctl, tty_write, etc.).

Rename all the static functions so they have a 'serial2002_' prefix
to avoid any issues.

Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Cc: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>