ath79: D-Link DAP-2680: select QCA9984 firmware

The DAP-2680 has a QCA9984 radio [1], but the commit adding support
mistakenly adds the QCA99x0 firmware package. See forum topic [2].

[1] https://wikidevi.wi-cat.ru/D-Link_DAP-2680_rev_A1
[2] https://forum.openwrt.org/t/missing-5ghz-radio-on-dlink-dap-2680/

Fixes: 5b58710 ("ath79: add support for D-Link DAP-2680 A1")
Signed-off-by: Stijn Segers <foss@volatilesystems.org>
Tested-by: Alessandro Fellin <af.registrazioni@gmail.com>

target/linux/ath79/image/generic.mk

@@ -896,7 +896,7 @@ define Device/dlink_dap-2680-a1
   DEVICE_VENDOR := D-Link
   DEVICE_MODEL := DAP-2680
   DEVICE_VARIANT := A1
-  DEVICE_PACKAGES := ath10k-firmware-qca99x0-ct kmod-ath10k-ct
+  DEVICE_PACKAGES := ath10k-firmware-qca9984-ct kmod-ath10k-ct
   IMAGE_SIZE := 15232k
   DAP_SIGNATURE := wapac36_dkbs_dap2680
 endef