Allow gsid to read dm nodes from sysfs.

This is needed now that libfiemap_writer reads from dm/name to find
device-mapper names.

Bug: 134536978
Test: gsi_tool install
Change-Id: I10e1234f2ea39c92b43ace97fa76878358dfc476
diff --git a/private/gsid.te b/private/gsid.te
index 1a35a4b..73b93fc 100644
--- a/private/gsid.te
+++ b/private/gsid.te
@@ -20,7 +20,7 @@
 # libfiemap_writer uses sysfs to derive the bottom of a device-mapper stacking.
 # This requires traversing /sys/block/dm-N/slaves/* and reading the list of
 # file names.
-allow gsid sysfs_dm:dir r_dir_perms;
+r_dir_file(gsid, sysfs_dm)
 
 # Needed to read fstab, which is used to validate that system verity does not
 # use check_once_at_most for sdcard installs. (Note: proc_cmdline is needed