Replace 'cpuset' init option with 'writepid'

The 'cpuset' option is not being upstreamed as expected and instead
we should be using the more generic 'writepid' option with the full
cpuset file path.

Bug: 35313295
Test: None
Change-Id: I451679192bad664b253b07942d78fb288980940f
diff --git a/services/vr/bufferhubd/bufferhubd.rc b/services/vr/bufferhubd/bufferhubd.rc
index ceedf1a..65b7293 100644
--- a/services/vr/bufferhubd/bufferhubd.rc
+++ b/services/vr/bufferhubd/bufferhubd.rc
@@ -2,5 +2,5 @@
   class core
   user system
   group system
-  cpuset /
+  writepid /dev/cpuset/tasks