net/mlx5e: TC, skip peer flow cleanup when LAG seq is unavailable

In the Linux kernel, the following vulnerability has been resolved:

net/mlx5e: TC, skip peer flow cleanup when LAG seq is unavailable

mlx5_lag_get_dev_seq() will return error when the peer isn't in the LAG
or when no device is marked as master. Result bad memory access and kernel
crash[1].

Hence, skip the peer when lookup fails.

Note: In case there are peer flows, they are cleaned before LAG cleared
the master mark.

[1]
RIP: 0010:mlx5e_tc_del_fdb_peers_flow+0x3d/0x350 [mlx5_core]
Call Trace:
<TASK>
mlx5e_tc_clean_fdb_peer_flows+0xc1/0x130 [mlx5_core]
mlx5_esw_offloads_unpair+0x3a/0x400 [mlx5_core]
mlx5_esw_offloads_devcom_event+0xee/0x360 [mlx5_core]
mlx5_devcom_send_event+0x7a/0x140 [mlx5_core]
mlx5_esw_offloads_devcom_cleanup+0x2f/0x90 [mlx5_core]
mlx5e_tc_esw_cleanup+0x28/0xf0 [mlx5_core]
mlx5e_rep_tc_cleanup+0x19/0x30 [mlx5_core]
mlx5e_cleanup_uplink_rep_tx+0x36/0x40 [mlx5_core]
mlx5e_cleanup_rep_tx+0x55/0x60 [mlx5_core]
mlx5e_detach_netdev+0x96/0xf0 [mlx5_core]
mlx5e_netdev_change_profile+0x5b/0x120 [mlx5_core]
mlx5e_netdev_attach_nic_profile+0x1b/0x30 [mlx5_core]
mlx5e_vport_rep_unload+0xdd/0x110 [mlx5_core]
__esw_offloads_unload_rep+0x81/0xb0 [mlx5_core]
mlx5_eswitch_unregister_vport_reps+0x1d7/0x220 [mlx5_core]
mlx5e_rep_remove+0x22/0x30 [mlx5_core]
device_release_driver_internal+0x194/0x1f0
bus_remove_device+0xe8/0x1b0
device_del+0x159/0x3c0
mlx5_rescan_drivers_locked+0xbc/0x2d0 [mlx5_core]
mlx5_unregister_device+0x54/0x80 [mlx5_core]
mlx5_uninit_one+0x73/0x130 [mlx5_core]
remove_one+0x78/0xe0 [mlx5_core]
pci_device_remove+0x39/0xa0