USB: add 5372:2303 to pl2303

This patch adds the "Superial" USB-Serial converter to pl2303 so that it
is detected, by the correct driver.  Adds the relevant vendor:product
(5372:2303) to the device tables in pl2303.c & pl2303.h.  The patch has
been tested against 2.6.24-22-generic.

Signed-off-by: Matthew D Arnold <matthew.arnold-1@uts.edu.au>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>