ruby: Fix prefetching for MESI_CMP_Directory

Transitions from present on PF_Ifetch were missing, causing a crash when
prefetching is enabled.

Committed by: Nilay Vaish <nilay@cs.wisc.edu>

src/mem/protocol/MESI_CMP_directory-L1cache.sm

@@ -940,7 +940,7 @@ machine(L1Cache, "MESI Directory L1 Cache CMP")
   }
 
   transition({S,E,M,IS,IM,SM,IS_I,M_I,SINK_WB_ACK,PF_IS,PF_IM},
-             {PF_Load, PF_Store}) {
+             {PF_Load, PF_Store, PF_Ifetch}) {
       pq_popPrefetchQueue;
   }