NFSD: Remove a layering violation when encoding lock_denied

An XDR encoder is responsible for marshaling results, not releasing
memory that was allocated by the upper layer. We have .op_release
for that purpose.

Move the release of the ld_owner.data string to op_release functions
for LOCK and LOCKT.

Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>