Update Makefile to build from source in fs/autofs instead of fs/autofs4.

Link: http://lkml.kernel.org/r/152626706824.28589.1915028175544560855.stgit@pluto.themaw.netSigned-off-by: Ian Kent <raven@themaw.net>
Cc: Al Viro <viro@ZenIV.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>