Currently it does not do so if the RPC call failed to start. Fix is to
move the decrement of plh_block_lgets into nfs4_layoutreturn_release.

Also remove a redundant test of task->tk_status in nfs4_layoutreturn_done:
if lrp->res.lrs_present is set, then obviously the RPC call succeeded.
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>