net/mlx5: DR, prevent potential error pointer dereference

The dr_domain_add_vport_cap() function generally returns NULL on error
but sometimes we want it to return ERR_PTR(-EBUSY) so the caller can
retry.  The problem here is that "ret" can be either -EBUSY or -ENOMEM
and if it's and -ENOMEM then the error pointer is propogated back and
eventually dereferenced in dr_ste_v0_build_src_gvmi_qpn_tag().

Fixes: 11a45de ("net/mlx5: DR, Add support for SF vports")
Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
Reviewed-by: Tariq Toukan <tariqt@nvidia.com>
Link: https://patch.msgid.link/07477254-e179-43e2-b1b3-3b9db4674195@stanley.mountain
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Author: Dan Carpenter

drivers/net/ethernet/mellanox/mlx5/core/steering/sws/dr_domain.c

@@ -297,7 +297,9 @@ dr_domain_add_vport_cap(struct mlx5dr_domain *dmn, u16 vport)
 	if (ret) {
 		mlx5dr_dbg(dmn, "Couldn't insert new vport into xarray (%d)\n", ret);
 		kvfree(vport_caps);
-		return ERR_PTR(ret);
+		if (ret == -EBUSY)
+			return ERR_PTR(-EBUSY);
+		return NULL;
 	}
 
 	return vport_caps;