char: moxa.c sparse annotation

The only use is to pass this to le16_to_cpu, declare as such
drivers/char/moxa.c:548:11: warning: cast to restricted __le16.

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