autofs4: comment typo: remove a a doubled word

Signed-off-by: NeilBrown <neilb@suse.de>
Acked-by: Ian Kent <raven@themaw.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>