autofs: change autofs4_expire_wait()/do_expire_wait() to take struct path

autofs: change autofs4_expire_wait()/do_expire_wait() to take struct path

In order to use the functions path_is_mountpoint() and path_has_submounts()
autofs needs to pass a struct path in several places.

Start by changing autofs4_expire_wait() and do_expire_wait() to take
a struct path instead of a struct dentry.

Link: http://lkml.kernel.org/r/20161011053408.27645.40091.stgit@pluto.themaw.net
Signed-off-by: Ian Kent <raven@themaw.net>
Cc: Al Viro <viro@ZenIV.linux.org.uk>
Cc: Eric W. Biederman <ebiederm@xmission.com>
Cc: Omar Sandoval <osandov@osandov.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>