autofs: fix "fix dev ioctl number range check"

autofs: fix "fix dev ioctl number range check"

102a340f had a typo that made the count macro negative (-13).
The acutal check used by ioctl is ((cmd - cmd_first) > COUNT),
so it needs to be positive (13).

* 102a340f is a commit in linux-next which hasn't been merged
to mainline upstream.

Link: http://lkml.kernel.org/r/20160831033420.9910.16809.stgit@pluto.themaw.net
Signed-off-by: Tomohiro Kusumi <kusumi.tomohiro@gmail.com>
Signed-off-by: Ian Kent <raven@themaw.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>