wifi: wl3501_cs: don't call kfree_skb() under spin_lock_irqsave()

It is not allowed to call kfree_skb() from hardware interrupt
context or with interrupts being disabled. So replace kfree_skb()
with dev_kfree_skb_irq() under spin_lock_irqsave(). Compile
tested only.

Fixes: 1da177e4 ("Linux-2.6.12-rc2")
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20221207150453.114742-1-yangyingliang@huawei.com