NFSD: Fix nfsd4_encode_fattr4() crasher

Ensure that args.acl is initialized early. It is used in an
unconditional call to kfree() on the way out of
nfsd4_encode_fattr4().
Reported-by: Scott Mayhew <smayhew@redhat.com>
Fixes: 83ab8678 ("NFSD: Add struct nfsd4_fattr_args")
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

fs/nfsd/nfs4xdr.c

@@ -3515,6 +3515,7 @@ nfsd4_encode_fattr4(struct svc_rqst *rqstp, struct xdr_stream *xdr,
 	args.exp = exp;
 	args.dentry = dentry;
 	args.ignore_crossmnt = (ignore_crossmnt != 0);
+	args.acl = NULL;
 
 	/*
 	 * Make a local copy of the attribute bitmap that can be modified.
@@ -3573,7 +3574,6 @@ nfsd4_encode_fattr4(struct svc_rqst *rqstp, struct xdr_stream *xdr,
 	} else
 		args.fhp = fhp;
 
-	args.acl = NULL;
 	if (attrmask[0] & FATTR4_WORD0_ACL) {
 		err = nfsd4_get_nfs4_acl(rqstp, dentry, &args.acl);
 		if (err == -EOPNOTSUPP)