NFS: Clean up nfs4_callback_layoutrecall()

In addition to removing the dprintk(), this patch also initializes "res"
to the default return value instead of doing this through an else
condition.

Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>