NFSD: clean up alloc_init_deleg()

Modify the conditional statement for null pointer check in the function
'alloc_init_deleg' to make this function more robust and clear. Otherwise,
this function may have potential pointer dereference problem in the future,
when modifying or expanding the nfs4_delegation structure.

Signed-off-by: Sicong Huang <huangsicong@iie.ac.cn>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

fs/nfsd/nfs4state.c

@@ -1160,6 +1160,7 @@ alloc_init_deleg(struct nfs4_client *clp, struct nfs4_file *fp,
 		 struct nfs4_clnt_odstate *odstate, u32 dl_type)
 {
 	struct nfs4_delegation *dp;
+	struct nfs4_stid *stid;
 	long n;
 
 	dprintk("NFSD alloc_init_deleg\n");
@@ -1168,9 +1169,10 @@ alloc_init_deleg(struct nfs4_client *clp, struct nfs4_file *fp,
 		goto out_dec;
 	if (delegation_blocked(&fp->fi_fhandle))
 		goto out_dec;
-	dp = delegstateid(nfs4_alloc_stid(clp, deleg_slab, nfs4_free_deleg));
-	if (dp == NULL)
+	stid = nfs4_alloc_stid(clp, deleg_slab, nfs4_free_deleg);
+	if (stid == NULL)
 		goto out_dec;
+	dp = delegstateid(stid);
 
 	/*
 	 * delegation seqid's are never incremented.  The 4.1 special