ath79: fix ath10k caldata extraction on some D-Link DIR-842 C3 devices

ath79: fix ath10k caldata extraction on some D-Link DIR-842 C3 devices

According to forum threads [0][1] and a report on IRC by Doc-Saintly
some of those boards have calibration data in a different place. Only
one alternative location is known.

Without proper board calibration data (board.bin having all 0xff bytes)
ath10k firmware still tries to load but crashes on startup with a
confusing error message.

If you're applying this patch manually on your device do not forget to
remove /lib/firmware/ath10k/pre-cal-pci-0000:00:00.0.bin and reboot to
force caldata re-extraction.

[0] https://forum.openwrt.org/t/support-for-d-link-dir842-rev-c3/41654
[1] https://forum.openwrt.org/t/d-link-dir-842-cant-access-firmware-upload-form/65454

Signed-off-by: Paul Fertser <fercerpav@gmail.com>