nfscl: Simplify the deleg argument for nfscl_deleg()

The deleg argument to nfscl_deleg() is a "struct nfscldeleg **"
although the returned pointer value is never used by callers.

This patch changes the argument to "struct nfscldeleg *" to
simplify the call and avoid any confusion w.r.t. use of the
returned value.

This patch should not create any NFS semantics change.