Char: mxser, update documentation

Update Documentation/moxa-smartio to the later document from the mxser
package.
Signed-off-by: NJiri Slaby <jirislaby@gmail.com>
Acked-by: NAlan Cox <alan@redhat.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>