ath6kl: remove -D__CHECK_ENDIAN__ from Makefile

As drivers/net/wireless/ath/Makefile contains the flag to enable
endian checks there's no need to have it in ath6kl makefile anymore.
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>

drivers/net/wireless/ath/ath6kl/Makefile

@@ -33,5 +33,3 @@ ath6kl-y += txrx.o
 ath6kl-y += wmi.o
 ath6kl-y += sdio.o
 ath6kl-$(CONFIG_NL80211_TESTMODE) += testmode.o
-
-ccflags-y += -D__CHECK_ENDIAN__