crypto: xcbc - Fix incorrect error value when creating instance

If shash_alloc_instance() fails, we return the wrong error value.
This patch fixes it.
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

crypto/xcbc.c

@@ -252,6 +252,7 @@ static int xcbc_create(struct crypto_template *tmpl, struct rtattr **tb)
 	}
 
 	inst = shash_alloc_instance("xcbc", alg);
+	err = PTR_ERR(inst);
 	if (IS_ERR(inst))
 		goto out_put_alg;