ath10k: fix kernel panic while shutting down AP

The commit 64badcb6d645 ("ath10k: workaround fw beaconing bug") is freeing
DMA-coherent memory in irq context which is hitting BUG ON in ARM platforms.
Fix this by moving dma_free out of spin lock.

kernel BUG at mm/vmalloc.c:1512!
Internal error: Oops - BUG: 0 [#1] PREEMPT SMP ARM
CPU: 0 PID: 722 Comm: hostapd Not tainted 3.14.0 #3
task: dd58b840 ti: da6a6000 task.ti: da6a6000
PC is at vunmap+0x24/0x34
LR is at __arm_dma_free.isra.21+0x12c/0x190
[<c02a97d0>] (vunmap) from [<c021f81c>] (__arm_dma_free.isra.21+0x12c/0x190)
[<c021f81c>] (__arm_dma_free.isra.21) from [<bf3b2440>]
			(ath10k_mac_vif_beacon_free+0xf4/0x100 [ath10k_core])
[<bf3b2440>] (ath10k_mac_vif_beacon_free [ath10k_core]) from [<bf3b2490>]
			(ath10k_remove_interface+0x44/0x1ec [ath10k_core])
[<bf3b2490>] (ath10k_remove_interface [ath10k_core]) from [<bf3352e4>]
			(ieee80211_add_virtual_monitor+0x9d8/0x9f0 [mac80211])
[<bf3352e4>] (ieee80211_add_virtual_monitor [mac80211]) from [<bf33530c>]
			(ieee80211_stop+0x10/0x18 [mac80211])
[<bf33530c>] (ieee80211_stop [mac80211]) from [<c040d144>]
			(__dev_close_many+0x9c/0xcc)

Cc: Michal Kazior <michal.kazior@tieto.com>
Signed-off-by: Rajkumar Manoharan <rmanohar@qti.qualcomm.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>