charger: read permissions to /sys/power/state

Fixes these denials:
avc:  denied  { read } for  pid=585 comm="charger" name="state"
dev="sysfs" ino=18844 scontext=u:r:charger:s0
tcontext=u:object_r:sysfs_power:s0 tclass=file permissive=1

avc:  denied  { open } for  pid=585 comm="charger"
path="/sys/power/state" dev="sysfs" ino=18844 scontext=u:r:charger:s0
tcontext=u:object_r:sysfs_power:s0 tclass=file permissive=1

Test: above denials not observed in charger mode.
Change-Id: I5660e63315fada7f24d6cfe2e0bd2b383b556670

public/charger.te

@@ -17,8 +17,8 @@ wakelock_use(charger)
 
 allow charger self:netlink_kobject_uevent_socket create_socket_perms_no_ioctl;
 
-# Write to /sys/power/state
-allow charger sysfs_power:file write;
+# Read/write to /sys/power/state
+allow charger sysfs_power:file rw_file_perms;
 
 allow charger sysfs_batteryinfo:file r_file_perms;