autofs: update MAINTAINERS entry for autofs

Update the autofs entry in MAINTAINERS to reflect the rename of autofs4
to autofs.

Link: http://lkml.kernel.org/r/152626709611.28589.456596640024354223.stgit@pluto.themaw.net


Signed-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>