fix autofs regression caused by follow_managed() changes
we need to reload ->d_flags after the call of ->d_manage() - the thing
might've been called with dentry still negative and have the damn thing
turned positive while we'd waited.
Fixes: d41efb522e90 "fs/namei.c: pull positivity check into follow_managed()" Reported-by: Ian Kent <raven@themaw.net> Tested-by: Ian Kent <raven@themaw.net> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>