sepolicy: Label ro.config.ring_notification_vol_steps

Change-Id: I759c93297be64c26591e2d620355ad8bbc2aef22
diff --git a/common/private/property_contexts b/common/private/property_contexts
new file mode 100644
index 0000000..0b62bdd
--- /dev/null
+++ b/common/private/property_contexts
@@ -0,0 +1 @@
+ro.config.ring_notification_vol_steps u:object_r:systemsound_config_prop:s0 exact string