memory system: fix functional access bug.

Make sure not to keep processing functional accesses
after they've been responded to.
Also use checkFunctional() return value instead of checking
packet command field where possible, mostly just for consistency.

--HG--
extra : convert_revision : 29fc76bc18731bd93a4ed05a281297827028ef75

src/mem/cache/base_cache.cc

@@ -81,9 +81,9 @@ BaseCache::CachePort::deviceBlockSize()
 void
 BaseCache::CachePort::checkAndSendFunctional(PacketPtr pkt)
 {
-    checkFunctional(pkt);
-    if (!pkt->isResponse())
+    if (!checkFunctional(pkt)) {
         sendFunctional(pkt);
+    }
 }