Update kernel permissions to pass libdm snapshot unit test

Bug: 143654050
Test: libdm_test
Change-Id: I671937b3f3144066bf3529e11ad19a73b0eb685e
diff --git a/public/kernel.te b/public/kernel.te
index 46864b8..42fe2c4 100644
--- a/public/kernel.te
+++ b/public/kernel.te
@@ -107,7 +107,7 @@
 ')
 
 # required by VTS lidbm unit test
-allow kernel appdomain_tmpfs:file read;
+allow kernel appdomain_tmpfs:file { read write };
 
 ###
 ### neverallow rules