NFS: Have nfs41_proc_reclaim_complete() call nfs4_call_sync_custom()

An async call followed by an rpc_wait_for_completion() is basically the
same as a synchronous call, so we can use nfs4_call_sync_custom() to
keep our custom callback ops and the RPC_TASK_NO_ROUND_ROBIN flag.

Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>