RDMA/mlx5: Fix typo in destroy_mkey inbox

Set mkey_index to the correct place when preparing the destroy_mkey inbox,
this will fix the following syndrome:

 mlx5_core 0000:08:00.0: mlx5_cmd_check:782:(pid 980716): DEALLOC_PD(0x801)
 op_mod(0x0) failed, status bad resource state(0x9), syndrome (0x31b635)

Link: https://lore.kernel.org/r/20210311142024.1282004-1-leon@kernel.org
Fixes: 1368ead0 ("RDMA/mlx5: Use strict get/set operations for obj_id")
Reviewed-by: Ido Kalir <idok@mellanox.com>
Reviewed-by: Yishai Hadas <yishaih@nvidia.com>
Signed-off-by: Mark Zhang <markzhang@nvidia.com>
Signed-off-by: Leon Romanovsky <leonro@nvidia.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>

drivers/infiniband/hw/mlx5/devx.c

@@ -1116,7 +1116,7 @@ static void devx_obj_build_destroy_cmd(void *in, void *out, void *din,
 	case MLX5_CMD_OP_CREATE_MKEY:
 		MLX5_SET(destroy_mkey_in, din, opcode,
 			 MLX5_CMD_OP_DESTROY_MKEY);
-		MLX5_SET(destroy_mkey_in, in, mkey_index, *obj_id);
+		MLX5_SET(destroy_mkey_in, din, mkey_index, *obj_id);
 		break;
 	case MLX5_CMD_OP_CREATE_CQ:
 		MLX5_SET(destroy_cq_in, din, opcode, MLX5_CMD_OP_DESTROY_CQ);