mem-cache: a missing cast was truncating addresses

High bits were truncated when computing the block address

Change-Id: Iab2a4c6063ece2d1d4c24ce5686045a6d6d35434
Reviewed-on: https://gem5-review.googlesource.com/c/14415
Reviewed-by: Nikos Nikoleris <nikos.nikoleris@arm.com>
Reviewed-by: Daniel Carvalho <odanrc@yahoo.com.br>
Maintainer: Nikos Nikoleris <nikos.nikoleris@arm.com>

src/mem/cache/prefetch/base.cc

@@ -140,7 +140,7 @@ BasePrefetcher::samePage(Addr a, Addr b) const
 Addr
 BasePrefetcher::blockAddress(Addr a) const
 {
-    return a & ~(blkSize-1);
+    return a & ~((Addr)blkSize-1);
 }
 
 Addr