Allow dumpstate to read sysfs_loop files.

This prevents denials while taking a bugreport.

Bug: 116711254
Test: cts-tradefed run cts -m CtsSecurityHostTestCases -t
android.security.cts.SELinuxHostTest#testNoBugreportDenials

Change-Id: Ie190bfa62cf5aa172ebfff8bfd82dea2a7d1a016

public/dumpstate.te

@@ -90,6 +90,7 @@ allow dumpstate sysfs_type:dir r_dir_perms;
 
 allow dumpstate {
   sysfs_dm
+  sysfs_loop
   sysfs_usb
   sysfs_zram
 }:file r_file_perms;