Fix aosp healthd.

We only need this change for aosp devices. Internal sepolicy for healthd
domain is different and does not need this.

Addresses this denial:
avc: denied { open } for path="/sys/class/power_supply" dev="sysfs"
ino=25340 scontext=u:r:healthd:s0 tcontext=u:object_r:sysfs:s0
tclass=dir permissive=1

Test: $OUT/vendor/etc/selinux/precompiled_sepolicy contains the new
permission.
Change-Id: Ie47c231af800026fd9d8a1f752253bb338768c13

public/healthd.te

@@ -7,6 +7,8 @@ allow healthd kmsg_device:chr_file rw_file_perms;
 
 # Read access to pseudo filesystems.
 allow healthd sysfs_type:dir search;
+# Allow to read /sys/class/power_supply directory.
+allow healthd sysfs:dir r_dir_perms;
 r_dir_file(healthd, rootfs)
 r_dir_file(healthd, cgroup)