procrank: fix procrank when run from dumpstate

Commit a1913988 added a new
SELinux label to /system/xbin/procrank, which had the effect of
preventing dumpstate from executing procrank. Allow dumpstate
to execute procrank.

Bug: 18342188
Change-Id: If5b781db0d3af34912f3c803b7fa73d53120f3ba