[PATCH] autofs4: remove update_atime unused function

Remove the update of i_atime from autofs4 in favour of having VFS update it.
i_atime is never used for expire in autofs4.

Signed-off-by: Ian Kent <raven@themaw.net>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>