dpaa2-switch: fix VLAN upper check not rejecting bridge join

[ Upstream commit ed2294f ]

The blamed commit refactored the prechangeupper event handling but
failed to actually return an error in case
dpaa2_switch_prevent_bridging_with_8021q_upper() detected a 802.1q upper
on a port which tries to join a bridge. Fix this by returning err
instead of 0.

Fixes: 45035fe ("net: dpaa2-switch: refactor prechangeupper sanity checks")
Signed-off-by: Ioana Ciornei <ioana.ciornei@nxp.com>
Link: https://patch.msgid.link/20260616105430.3725910-1-ioana.ciornei@nxp.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

Author: IoanaCiornei

drivers/net/ethernet/freescale/dpaa2/dpaa2-switch.c

@@ -2180,7 +2180,7 @@ dpaa2_switch_prechangeupper_sanity_checks(struct net_device *netdev,
 	if (err) {
 		NL_SET_ERR_MSG_MOD(extack,
 				   "Cannot join a bridge while VLAN uppers are present");
-		return 0;
+		return err;
 	}
 
 	return 0;