init: allow read of /sys/devices/virtual/block/zram

Commit erroneously 55039509 removed init's read access to
/sys/devices/virtual/block/zram*. Restore access.

Test: cat /proc/meminfo
    ...
    SwapTotal:        524284 kB
    SwapFree:         524284 kB
    ...
Bug: 71510938

Change-Id: I20268168caa541a7dafa1e32339641095e1e524b

public/init.te

@@ -305,13 +305,16 @@ allow init {
   sysfs_android_usb
   sysfs_leds
   sysfs_power
-  sysfs_zram
 }:file w_file_perms;
 
 allow init {
   sysfs_dt_firmware_android
 }:file r_file_perms;
 
+allow init {
+  sysfs_zram
+}:file rw_file_perms;
+
 # init chmod/chown access to /sys files.
 allow init {
   sysfs_android_usb