Fix MTP sync

Address the following denial:
avc: denied { use } for path="/storage/emulated/0/305512.pdf" dev="fuse"
ino=239 scontext=u:r:kernel:s0 tcontext=u:r:priv_app:s0:c512,c768 tclass=fd
permissive=0

Bug: 25068662
Change-Id: Ic29d9569ff387dfd411363db751c3642572c8e85

kernel.te

@@ -42,7 +42,7 @@ allow kernel self:security setcheckreqprot;
 
 # MTP sync (b/15835289)
 # kernel thread "loop0", used by the loop block device, for ASECs (b/17158723)
-allow kernel untrusted_app:fd use;
+allow kernel { priv_app untrusted_app }:fd use;
 allow kernel sdcard_type:file { read write };
 
 # Allow the kernel to read OBB files from app directories. (b/17428116)