USB: ftd_sio: cleanups and updates for new termios work

- Remove can't happen tests
- Rework speed validation in terms of baud rates not CBAUD bits
- Report speed set (or chosen)
- Minor termios correctness

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>