autofs: use AUTOFS_DEV_IOCTL_SIZE

autofs: use AUTOFS_DEV_IOCTL_SIZE

Use a macro which defines misc-dev ioctl parameter size (excluding a path
beyond &path[0]) since it's been used to initialize and copy this
structure ever since it first appeared in 8d7b48e0 in 2008.

(or simply get rid of this if this is just unnecessary abstraction when
all it needs is sizeof(struct autofs_dev_ioctl))

Edit: raven@themaw.net
That's a good point but I'd prefer to keep the macro define.
End edit: raven@themaw.net

Link: http://lkml.kernel.org/r/150285068577.4670.2599968823770600622.stgit@pluto.themaw.net
Signed-off-by: Tomohiro Kusumi <tkusumi@tuxera.com>
Signed-off-by: Ian Kent <raven@themaw.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>