Set the permissions of wifi supplicant file so that system can access it.
Create the required directories and set the correct owner and permissions.
diff --git a/rootdir/init.rc b/rootdir/init.rc
index ac066fa..d318aa3 100644
--- a/rootdir/init.rc
+++ b/rootdir/init.rc
@@ -78,6 +78,11 @@
mkdir /data/misc/keystore 0770 keystore keystore
mkdir /data/misc/vpn 0770 system system
mkdir /data/misc/vpn/profiles 0770 system system
+ mkdir /data/misc/wifi 0770 wifi system
+ chown wifi system /data/misc/wifi
+ touch /data/misc/wifi/wpa_supplicant.conf
+ chmod 0660 /data/misc/wifi/wpa_supplicant.conf
+ chown wifi system /data/misc/wifi/wpa_supplicant.conf
mkdir /data/local 0771 shell shell
mkdir /data/local/tmp 0771 shell shell
mkdir /data/data 0771 system system