package/rtl8821au: set CONFIG_RTL8821AU properly

Due to a recent update in the code, CONFIG_RTL8821AU=m is the expected
kernel configuration environment variable to be set, not
CONFIG_RTL8812AU_8821AU=m as was previously set.

Presently the package does effectively nothing.

Signed-off-by: Christian Stewart <christian@paral.in>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/rtl8821au/rtl8821au.mk

@@ -10,7 +10,7 @@ RTL8821AU_LICENSE = GPLv2, proprietary (rtl8821au.bin firmware)
 RTL8821AU_LICENSE_FILES = COPYING
 
 RTL8821AU_MODULE_MAKE_OPTS = \
-	CONFIG_RTL8812AU_8821AU=m \
+	CONFIG_RTL8821AU=m \
 	KVER=$(LINUX_VERSION_PROBED) \
 	USER_EXTRA_CFLAGS=-DCONFIG_$(call qstrip,$(BR2_ENDIAN))_ENDIAN