net: microchip: sparx5: Improve the error handling for linked rules

Ensure that an error is returned if the VCAP instance was not found.
The chain offset (diff) is allowed to be zero as this just means that the
user did not request rules to be linked.
Signed-off-by: Steen Hegelund <steen.hegelund@microchip.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

drivers/net/ethernet/microchip/sparx5/sparx5_tc_flower.c

@@ -551,12 +551,16 @@ static int sparx5_tc_add_rule_link(struct vcap_control *vctrl,
 	struct vcap_admin *to_admin = vcap_find_admin(vctrl, to_cid);
 	int diff, err = 0;
 
-	diff = vcap_chain_offset(vctrl, from_cid, to_cid);
-	if (!(to_admin && diff > 0)) {
+	if (!to_admin) {
 		pr_err("%s:%d: unsupported chain direction: %d\n",
 		       __func__, __LINE__, to_cid);
 		return -EINVAL;
 	}
+
+	diff = vcap_chain_offset(vctrl, from_cid, to_cid);
+	if (!diff)
+		return 0;
+
 	if (admin->vtype == VCAP_TYPE_IS0 &&
 	    to_admin->vtype == VCAP_TYPE_IS0) {
 		/* Between IS0 instances the G_IDX value is used */