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>

target/linux/ath79/generic/base-files/etc/hotplug.d/firmware/11-ath10k-caldata

@@ -169,13 +169,18 @@ case "$FIRMWARE" in
 		;;
 	dlink,dir-842-c1|\
 	dlink,dir-842-c2|\
-	dlink,dir-842-c3|\
+	dlink,dir-842-c3)
+		caldata_extract "art" 0x5000 0x2f20
+		caldata_valid "202f" || caldata_extract "reserved" 0x15000 0x2f20
+		ath10k_patch_mac $(mtd_get_mac_ascii devdata wlan5mac)
+		ln -sf /lib/firmware/ath10k/pre-cal-pci-0000\:00\:00.0.bin \
+			/lib/firmware/ath10k/QCA9888/hw2.0/board.bin
+		;;
 	nec,wg1200cr)
 		caldata_extract "art" 0x5000 0x2f20
 		ath10k_patch_mac $(mtd_get_mac_ascii devdata wlan5mac)
 		ln -sf /lib/firmware/ath10k/pre-cal-pci-0000\:00\:00.0.bin \
 			/lib/firmware/ath10k/QCA9888/hw2.0/board.bin
-		;;
 	netgear,ex6400|\
 	netgear,ex7300)
 		caldata_extract "caldata" 0x5000 0x2f20