mt76: dma: fix possible deadlock running mt76_dma_cleanup

Fix the following possible deadlock reported by lockdep disabling BH
running mt76_free_pending_txwi()

================================
WARNING: inconsistent lock state
5.9.0-rc6 Freescale#14 Not tainted
--------------------------------
inconsistent {IN-SOFTIRQ-W} -> {SOFTIRQ-ON-W} usage.
rmmod/1227 [HC0[0]:SC0[0]:HE1:SE1] takes:
ffff888156a83530 (&dev->lock#2){+.?.}-{2:2}, at: mt76_dma_cleanup+0x125/0x150 [mt76]
{IN-SOFTIRQ-W} state was registered at:
  __lock_acquire+0x20c/0x6b0
  lock_acquire+0x9d/0x220
  _raw_spin_lock+0x2c/0x70
  mt76_dma_tx_cleanup+0xc7/0x200 [mt76]
  mt76x02_poll_tx+0x31/0xb0 [mt76x02_lib]
  napi_poll+0x3a/0x100
  net_rx_action+0xa8/0x200
  __do_softirq+0xc4/0x430
  asm_call_on_stack+0xf/0x20
  do_softirq_own_stack+0x49/0x60
  irq_exit_rcu+0x9a/0xd0
  common_interrupt+0xa4/0x190
  asm_common_interrupt+0x1e/0x40
irq event stamp: 9915
hardirqs last  enabled at (9915): [<ffffffff8124e286>] __free_pages_ok+0x336/0x3b0
hardirqs last disabled at (9914): [<ffffffff8124e24e>] __free_pages_ok+0x2fe/0x3b0
softirqs last  enabled at (9912): [<ffffffffa03aa672>] mt76_dma_rx_cleanup+0xa2/0x120 [mt76]
softirqs last disabled at (9846): [<ffffffffa03aa5ea>] mt76_dma_rx_cleanup+0x1a/0x120 [mt76]

other info that might help us debug this:
 Possible unsafe locking scenario:

       CPU0
       ----
  lock(&dev->lock#2);
  <Interrupt>
    lock(&dev->lock#2);

 *** DEADLOCK ***

1 lock held by rmmod/1227:
 #0: ffff88815b5eb240 (&dev->mutex){....}-{3:3}, at: driver_detach+0xb5/0x110

stack backtrace:
CPU: 1 PID: 1227 Comm: rmmod Kdump: loaded Not tainted 5.9.0-rc6-wdn-src+ Freescale#14
Hardware name: Dell Inc. Studio XPS 1340/0K183D, BIOS A11 09/08/2009
Call Trace:
 dump_stack+0x77/0xa0
 mark_lock_irq.cold+0x15/0x39
 mark_lock+0x1fc/0x500
 mark_usage+0xc7/0x140
 __lock_acquire+0x20c/0x6b0
 ? find_held_lock+0x2b/0x80
 ? sched_clock_cpu+0xc/0xb0
 lock_acquire+0x9d/0x220
 ? mt76_dma_cleanup+0x125/0x150 [mt76]
 _raw_spin_lock+0x2c/0x70
 ? mt76_dma_cleanup+0x125/0x150 [mt76]
 mt76_dma_cleanup+0x125/0x150 [mt76]
 mt76x2_cleanup+0x5a/0x70 [mt76x2e]
 mt76x2e_remove+0x18/0x30 [mt76x2e]
 pci_device_remove+0x36/0xa0
 __device_release_driver+0x16c/0x220
 driver_detach+0xcf/0x110
 bus_remove_driver+0x56/0xca
 pci_unregister_driver+0x36/0x80
 __do_sys_delete_module.constprop.0+0x127/0x200
 ? syscall_enter_from_user_mode+0x1d/0x50
 ? trace_hardirqs_on+0x1c/0xe0
 do_syscall_64+0x33/0x80
 entry_SYSCALL_64_after_hwframe+0x44/0xa9
RIP: 0033:0x7ff0da54e36b
Code: 73 01 c3 48 8b 0d 2d 0b 0c 00 f7 d8 64 89 01 48 83 c8 ff c3 66 2e 0f 1f 84 00 00 00 00 00 90 f3 0f 1e fa b8 b0 00 00 00 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d fd 0a 0c 00 f7 d8 64 89 01 48

Fixes: dd57a95 ("mt76: move txwi handling code to dma.c, since it is mmio specific")
Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
Signed-off-by: Felix Fietkau <nbd@nbd.name>

drivers/net/wireless/mediatek/mt76/dma.c

@@ -72,9 +72,11 @@ mt76_free_pending_txwi(struct mt76_dev *dev)
 {
 	struct mt76_txwi_cache *t;
 
+	local_bh_disable();
 	while ((t = __mt76_get_txwi(dev)) != NULL)
 		dma_unmap_single(dev->dev, t->dma_addr, dev->drv->txwi_size,
 				 DMA_TO_DEVICE);
+	local_bh_enable();
 }
 
 static int