net/mlx5: Fix variable not being completed when function returns

When cmd_alloc_index(), fails cmd_work_handler() needs
to complete ent->slotted before returning early.
Otherwise the task which issued the command may hang:

   mlx5_core 0000:01:00.0: cmd_work_handler:877:(pid 3880418): failed to allocate command entry
   INFO: task kworker/13:2:4055883 blocked for more than 120 seconds.
         Not tainted 4.19.90-25.44.v2101.ky10.aarch64 #1
   "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
   kworker/13:2    D    0 4055883      2 0x00000228
   Workqueue: events mlx5e_tx_dim_work [mlx5_core]
   Call trace:
      __switch_to+0xe8/0x150
      __schedule+0x2a8/0x9b8
      schedule+0x2c/0x88
      schedule_timeout+0x204/0x478
      wait_for_common+0x154/0x250
      wait_for_completion+0x28/0x38
      cmd_exec+0x7a0/0xa00 [mlx5_core]
      mlx5_cmd_exec+0x54/0x80 [mlx5_core]
      mlx5_core_modify_cq+0x6c/0x80 [mlx5_core]
      mlx5_core_modify_cq_moderation+0xa0/0xb8 [mlx5_core]
      mlx5e_tx_dim_work+0x54/0x68 [mlx5_core]
      process_one_work+0x1b0/0x448
      worker_thread+0x54/0x468
      kthread+0x134/0x138
      ret_from_fork+0x10/0x18

Fixes: 485d65e ("net/mlx5: Add a timeout to acquire the command queue semaphore")
Signed-off-by: Chenguang Zhao <zhaochenguang@kylinos.cn>
Reviewed-by: Moshe Shemesh <moshe@nvidia.com>
Acked-by: Tariq Toukan <tariqt@nvidia.com>
Link: https://patch.msgid.link/20250108030009.68520-1-zhaochenguang@kylinos.cn
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

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

@@ -1013,6 +1013,7 @@ static void cmd_work_handler(struct work_struct *work)
 				complete(&ent->done);
 			}
 			up(&cmd->vars.sem);
+			complete(&ent->slotted);
 			return;
 		}
 	} else {