net/mlx5: Don't use already freed action pointer

The call to mlx5dr_action_destroy() releases "action" memory. That
pointer is set to miss_action later and generates the following smatch
error:

 drivers/net/ethernet/mellanox/mlx5/core/steering/fs_dr.c:53 set_miss_action()
 warn: 'action' was already freed.

Make sure that the pointer is always valid by setting NULL after destroy.

Fixes: 6a48faee ("net/mlx5: Add direct rule fs_cmd implementation")
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Leon Romanovsky <leonro@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>

drivers/net/ethernet/mellanox/mlx5/core/steering/fs_dr.c

@@ -44,11 +44,10 @@ static int set_miss_action(struct mlx5_flow_root_namespace *ns,
 	err = mlx5dr_table_set_miss_action(ft->fs_dr_table.dr_table, action);
 	if (err && action) {
 		err = mlx5dr_action_destroy(action);
-		if (err) {
-			action = NULL;
-			mlx5_core_err(ns->dev, "Failed to destroy action (%d)\n",
-				      err);
-		}
+		if (err)
+			mlx5_core_err(ns->dev,
+				      "Failed to destroy action (%d)\n", err);
+		action = NULL;
 	}
 	ft->fs_dr_table.miss_action = action;
 	if (old_miss_action) {