USB: pl2303: fixed handling of CS5 setting

This patch fixes the CS5 setting on the PL2303 USB-to-serial devices. CS5 has a
value of 0 and the CSIZE setting has been skipped altogether by the enclosing
if. Tested on 3.11.6 and the scope shows the correct output after the fix has
been applied.

Tagged to be added to stable, because it fixes a user visible driver bug and is
simple enough to backport easily.

Signed-off-by: Colin Leitner <colin.leitner@gmail.com>
Signed-off-by: Johan Hovold <jhovold@gmail.com>
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>