wl1251: add a missing spin_lock_init()

This fixes the following kernel warning:

 [ 5668.771453] BUG: spinlock bad magic on CPU#0, kworker/u2:3/9745
 [ 5668.771850]  lock: 0xce63ef20, .magic: 00000000, .owner: <none>/-1,
 .owner_cpu: 0
 [ 5668.772277] CPU: 0 PID: 9745 Comm: kworker/u2:3 Tainted: G        W
 4.12.0-03002-gec979a4-dirty #40
 [ 5668.772796] Hardware name: Nokia RX-51 board
 [ 5668.773071] Workqueue: phy1 wl1251_irq_work
 [ 5668.773345] [<c010c9e4>] (unwind_backtrace) from [<c010a274>]
 (show_stack+0x10/0x14)
 [ 5668.773803] [<c010a274>] (show_stack) from [<c01545a4>]
 (do_raw_spin_lock+0x6c/0xa0)
 [ 5668.774230] [<c01545a4>] (do_raw_spin_lock) from [<c06ca578>]
 (_raw_spin_lock_irqsave+0x10/0x18)
 [ 5668.774658] [<c06ca578>] (_raw_spin_lock_irqsave) from [<c048c010>]
 (wl1251_op_tx+0x38/0x5c)
 [ 5668.775115] [<c048c010>] (wl1251_op_tx) from [<c06a12e8>]
 (ieee80211_tx_frags+0x188/0x1c0)
 [ 5668.775543] [<c06a12e8>] (ieee80211_tx_frags) from [<c06a138c>]
 (__ieee80211_tx+0x6c/0x130)
 [ 5668.775970] [<c06a138c>] (__ieee80211_tx) from [<c06a3dbc>]
 (ieee80211_tx+0xdc/0x104)
 [ 5668.776367] [<c06a3dbc>] (ieee80211_tx) from [<c06a4af0>]
 (__ieee80211_subif_start_xmit+0x454/0x8c8)
 [ 5668.776824] [<c06a4af0>] (__ieee80211_subif_start_xmit) from
 [<c06a4f94>] (ieee80211_subif_start_xmit+0x30/0x2fc)
 [ 5668.777343] [<c06a4f94>] (ieee80211_subif_start_xmit) from
 [<c0578848>] (dev_hard_start_xmit+0x80/0x118)
...

    by adding the missing spin_lock_init().

Reported-by: Pavel Machek <pavel@ucw.cz>
Cc: Kalle Valo <kvalo@codeaurora.org>
Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
Acked-by: Pavel Machek <pavel@ucw.cz>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Signed-off-by: Pavel Machek <pavel@ucw.cz>
Cc: stable@kernel.org
Signed-off-by: David S. Miller <davem@davemloft.net>