USB: ch341: fix termios handling

The ch341 currently doesn't support most of the hardware setting.  So to keep
the termios data right we propogate the old termios hardware values back then
encode the speed.

Signed-off-by: Alan Cox <alan@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>