USB: serial: pl2303: fix line-speed handling on newer chips

USB: serial: pl2303: fix line-speed handling on newer chips

commit 979d9cbe75b922ab1695b8ad5576115774f72e62 upstream.

The latest chip family (HXN) apparently does not support setting the
line speed using divisors and instead needs to use the direct encoding
scheme for all rates.

This specifically enables 50, 110, 134, 200 bps and other rates not
supported by the original chip type.

Fixes: ebd09f1cd417 ("USB: serial: pl2303: add support for PL2303HXN")
Cc: stable@vger.kernel.org      # 5.5
Cc: Charles Yeh <charlesyeh522@gmail.com>
Signed-off-by: Johan Hovold <johan@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>