ath: fix SPDX tags

Commit ec8f24b7fa ("treewide: Add SPDX license identifier -
Makefile/Kconfig") marked various Makefiles and Kconfig files within ath
directories as GPL-2.0. But these modules and drivers are actually ISC:

* ath
* ar5523
* ath10k
* ath5k
* ath6kl
* ath9k
* wcn36xx
* wil6210

Fix SPDX tags accordingly.

Signed-off-by: Kalle Valo <kvalo@codeaurora.org>

drivers/net/wireless/ath/ath9k/Kconfig

@@ -1,4 +1,4 @@
-# SPDX-License-Identifier: GPL-2.0-only
+# SPDX-License-Identifier: ISC
 config ATH9K_HW
 	tristate
 config ATH9K_COMMON

drivers/net/wireless/ath/ath9k/Makefile

@@ -1,4 +1,4 @@
-# SPDX-License-Identifier: GPL-2.0
+# SPDX-License-Identifier: ISC
 ath9k-y +=	beacon.o \
 		gpio.o \
 		init.o \