ceph: set DCACHE_NOKEY_NAME in atomic open

ceph: set DCACHE_NOKEY_NAME in atomic open

Atomic open can act as a lookup if handed a dentry that is negative on
the MDS. Ensure that we set DCACHE_NOKEY_NAME on the dentry in
atomic_open, if we don't have the key for the parent. Otherwise, we can
end up validating the dentry inappropriately if someone later adds a
key.

Reviewed-by: Luís Henriques <lhenriques@suse.de>
Reviewed-by: Xiubo Li <xiubli@redhat.com>
Signed-off-by: Jeff Layton <jlayton@kernel.org>