Char: mxser, ioctl cleanup

- remove dead MOXA_GET_CONF (always returned -ENXIO)
- remove useless MOXA_GET_CUMAJOR (unused)
- use get/put_user instead of copy_from/to_user for simple types
- cleanup TIOCMIWAIT -- return -ERESTARTSYS on signal, move condition into
  separate function

Signed-off-by: Jiri Slaby <jirislaby@gmail.com>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Reviewed-by: Alan Cox <alan@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>