ath10k: fix crash during card removal

ath10k: fix crash during card removal

Usually when the firmware crashes we check for the value
'FW_IND_EVENT_PENDING' in 'FW_INDICATOR_ADDRESS' and proceed with
disabling the irq and dumping firmware 'crash dump'. Now
when the PCI card is unplugged from the device the PCI controller
seems to generate a spurious interrupt after some time which
was as treated a firmware crash and resulting in the below race
condition (and eventually crashing the system)

	ath10k_core_unregister -> ath10k_core_free_board_files

	...... device unplug spurious interrupt .........

	ath10k_pci_taklet -> ath10k_pci_fw_crashed_dump  ...etc

Clearly even after the firmware board files related data structure
is freed up we are getting a spurious interrupt from PCI with 0xfffffff
in the 'FW_INDICATOR_ADDRESS' resulting in scheduling of the pci tasklet
and doing a crash dump, printing f/w board related info resulting in the
below crash. Fix this by detecting this spurious interrupt in ath10k PCI
irq handler itself and return IRQ_NONE. Thanks to Michal Kazior for
helping us conclude the most appropriate fix.

Call trace:

 EIP is at ath10k_debug_print_board_info+0x39/0xb0
[ath10k_core]
EAX: 00000000 EBX: d4de15a0 ECX: 00000000 EDX: 00000064
ESI: f615ddd0 EDI: f8530000 EBP: f615de3c ESP: f615ddbc
 DS: 007b ES: 007b FS: 00d8 GS: 0000 SS: 0068
CR0: 80050033 CR2: 00000004 CR3: 01c0a000 CR4: 000006f0
Stack:
 f615ddd0 00000064 f8b4ecdd 00000000 00000000 00412f4e
00000000 00000000
00000000 00000000 00000000 00000000 00000000 00000000
00000000 00000000
 00000000 00000000 00000000 00000000 00000000 00000000
00000000 00000000
Call Trace:
  [<f8b1f517>] ath10k_print_driver_info+0x17/0x30
[ath10k_core]
[<f875463a>] ath10k_pci_fw_crashed_dump+0x7a/0xe0
[ath10k_pci]
[<f87549d0>] ath10k_pci_tasklet+0x70/0x90 [ath10k_pci]
[<c106151e>] tasklet_action+0x9e/0xb0

Cc: Michal Kazior <michal.kazior@tieto.com>
Signed-off-by: Mohammed Shafi Shajakhan <mohammed@qti.qualcomm.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>