spkm3: initialize hash

There's an initialization step here I missed.
Signed-off-by: NJ. Bruce Fields <bfields@citi.umich.edu>
Signed-off-by: NTrond Myklebust <Trond.Myklebust@netapp.com>

net/sunrpc/auth_gss/gss_spkm3_seal.c

@@ -169,6 +169,10 @@ make_spkm3_checksum(s32 cksumtype, struct xdr_netobj *key, char *header,
 	if (err)
 		goto out;
 
+	err = crypto_hash_init(&desc);
+	if (err)
+		goto out;
+
 	sg_set_buf(sg, header, hdrlen);
 	crypto_hash_update(&desc, sg, sg->length);