Fix permission of zram writeback and idle file

The default permission of "/sys/block/zram0/idle" and
"/sys/block/zram0/writeback" are "0200".

Adding read permission to the files does not make sense because reading
those files fail as EIO error.

We should keep permission as minimum as possible.

Bug: 117682284
Bug: 375432468
Test: ls -la /sys/block/zram0

Change-Id: I11ed5d9eee257002f4698edcd81de39d2c317ea1
diff --git a/rootdir/init.rc b/rootdir/init.rc
index eeafd4c..8284435 100644
--- a/rootdir/init.rc
+++ b/rootdir/init.rc
@@ -1127,9 +1127,9 @@
 
     # System server manages zram writeback
     chown root system /sys/block/zram0/idle
-    chmod 0664 /sys/block/zram0/idle
+    chmod 0220 /sys/block/zram0/idle
     chown root system /sys/block/zram0/writeback
-    chmod 0664 /sys/block/zram0/writeback
+    chmod 0220 /sys/block/zram0/writeback
 
     # to access F2FS sysfs on dm-<num> directly
     mkdir /dev/sys/fs/by-name 0755 system system