storaged: add permissions for dumpstate

The service "storaged" implememnts a dump() interface for
dumpsys, and thus it needs to write its state to the fd
provided by dumpstate.

To correct this, and fix dumpstate, allow the permission.

Fixes:
avc: denied { use } for pid=3298 comm="dumpsys" path="pipe:[33470]" dev="pipefs" ino=33470 scontext=u:r:storaged:s0 tcontext=u:r:dumpstate:s0 tclass=fd permissive=0

Test:
With a device that has storaged, issue the command:
$ adb shell dumpstate

Change-Id: I515e20f0328b6edc01ea2a7c53b1d3c4ca0e72ac
Signed-off-by: William Roberts <william.c.roberts@intel.com>