staging: wfx: fix potential use before init

staging: wfx: fix potential use before init

The trace below can appear:

    [83613.832200] INFO: trying to register non-static key.
    [83613.837248] the code is fine but needs lockdep annotation.
    [83613.842808] turning off the locking correctness validator.
    [83613.848375] CPU: 3 PID: 141 Comm: kworker/3:2H Tainted: G           O      5.6.13-silabs15 #2
    [83613.857019] Hardware name: BCM2835
    [83613.860605] Workqueue: events_highpri bh_work [wfx]
    [83613.865552] Backtrace:
    [83613.868041] [<c010f2cc>] (dump_backtrace) from [<c010f7b8>] (show_stack+0x20/0x24)
    [83613.881463] [<c010f798>] (show_stack) from [<c0d82138>] (dump_stack+0xe8/0x114)
    [83613.888882] [<c0d82050>] (dump_stack) from [<c01a02ec>] (register_lock_class+0x748/0x768)
    [83613.905035] [<c019fba4>] (register_lock_class) from [<c019da04>] (__lock_acquire+0x88/0x13dc)
    [83613.924192] [<c019d97c>] (__lock_acquire) from [<c019f6a4>] (lock_acquire+0xe8/0x274)
    [83613.942644] [<c019f5bc>] (lock_acquire) from [<c0daa5dc>] (_raw_spin_lock_irqsave+0x58/0x6c)
    [83613.961714] [<c0daa584>] (_raw_spin_lock_irqsave) from [<c0ab3248>] (skb_dequeue+0x24/0x78)
    [83613.974967] [<c0ab3224>] (skb_dequeue) from [<bf330db0>] (wfx_tx_queues_get+0x96c/0x1294 [wfx])
    [83613.989728] [<bf330444>] (wfx_tx_queues_get [wfx]) from [<bf320454>] (bh_work+0x454/0x26d8 [wfx])
    [83614.009337] [<bf320000>] (bh_work [wfx]) from [<c014c920>] (process_one_work+0x23c/0x7ec)
    [83614.028141] [<c014c6e4>] (process_one_work) from [<c014cf1c>] (worker_thread+0x4c/0x55c)
    [83614.046861] [<c014ced0>] (worker_thread) from [<c0154c04>] (kthread+0x138/0x168)
    [83614.064876] [<c0154acc>] (kthread) from [<c01010b4>] (ret_from_fork+0x14/0x20)
    [83614.072200] Exception stack(0xecad3fb0 to 0xecad3ff8)
    [83614.077323] 3fa0:                                     00000000 00000000 00000000 00000000
    [83614.085620] 3fc0: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
    [83614.093914] 3fe0: 00000000 00000000 00000000 00000000 00000013 00000000

Indeed, the code of wfx_add_interface() shows that the interface is
enabled to early. So, the spinlock associated with some skb_queue may
not yet initialized when wfx_tx_queues_get() is called.

Signed-off-by: Jérôme Pouiller <jerome.pouiller@silabs.com>
Link: https://lore.kernel.org/r/20200825085828.399505-8-Jerome.Pouiller@silabs.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>