net/mlx5: Fix potential sleeping in atomic context

Fixes the below flow of sleeping in atomic context by releasing
the RCU lock before calling to free_match_list.

build_match_list() <- disables preempt
-> free_match_list()
   -> tree_put_node()
      -> down_write_ref_node() <- take write lock

Fixes: 693c688 ("net/mlx5: Add hash table for flow groups in flow table")
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Maor Gottlieb <maorg@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>

drivers/net/ethernet/mellanox/mlx5/core/fs_core.c

@@ -1682,14 +1682,13 @@ static int build_match_list(struct match_list *match_head,
 
 		curr_match = kmalloc(sizeof(*curr_match), GFP_ATOMIC);
 		if (!curr_match) {
+			rcu_read_unlock();
 			free_match_list(match_head, ft_locked);
-			err = -ENOMEM;
-			goto out;
+			return -ENOMEM;
 		}
 		curr_match->g = g;
 		list_add_tail(&curr_match->list, &match_head->list);
 	}
-out:
 	rcu_read_unlock();
 	return err;
 }