nx: uscript: Fix cec_disable appending

Change-Id: Iaa6b7f840ea2855700ad33de3cd146683285b035

bootfiles/android_boot.txt

@@ -227,8 +227,8 @@ if test "${loader_rev}" != 0 -a ${ddr200_enable} = 1; then
 fi
 
 if test ${sku} = 2 -o ${cec_disable} = 1; then
-	echo HDMI-CEC disabled
-	setenv bootargs ${bootargs} cec_disable=1 androidboot.cec_disable=1
+	echoe HDMI-CEC disabled
+	setenv bootargs_extra ${bootargs_extra} cec_disable=1 androidboot.cec_disable=1
 fi
 
 # Disable WiFi VHT80 bonding.