nfsd: use ATTR_DELEG in nfsd4_finalize_deleg_timestamps()

When finalizing timestamps that have never been updated and preparing to
release the delegation lease, the notify_change() call can trigger a
delegation break, and fail to update the timestamps. When this happens,
there will be messages like this in dmesg:

[ 2709.375785] Unable to update timestamps on inode 00:39:263: -11

Since this code is going to release the lease just after updating the
timestamps, breaking the delegation is undesirable. Fix this by setting
ATTR_DELEG in ia_valid, in order to avoid the delegation break.

Fixes: e5e9b24ab8fa ("nfsd: freeze c/mtime updates with outstanding WRITE_ATTRS delegation")
Cc: stable@vger.kernel.org
Signed-off-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>