system_app.te: fix misleading comment

A comment within system_app.te implies that system_apps can read/write
the /data/data directory (and all subdirectories). The comment is
misleading. Fix the comment.

Test: comment only change. No test needed
Change-Id: I51b95f8b55ac89730a866d2a829326b276b11824
diff --git a/private/system_app.te b/private/system_app.te
index 5016a40..e0ed8c3 100644
--- a/private/system_app.te
+++ b/private/system_app.te
@@ -13,7 +13,7 @@
 # android.ui and system.ui
 allow system_app rootfs:dir getattr;
 
-# Read and write /data/data subdirectory.
+# read/write certain subdirectories of /data/data for system UID apps.
 allow system_app system_app_data_file:dir create_dir_perms;
 allow system_app system_app_data_file:{ file lnk_file } create_file_perms;