Subzero: Clean up some uses of *_cast<>.

src/IceCfg.cpp

Index: src/IceCfg.cpp
diff --git a/src/IceCfg.cpp b/src/IceCfg.cpp
index fe44ee73d456366a568faf58ca1d25a4f43625c0..6565667e7287f6c52b791f857732f3c91ba6d333 100644
--- a/src/IceCfg.cpp
+++ b/src/IceCfg.cpp
@@ -916,8 +916,7 @@ bool Cfg::validateLiveness() const {
           // of the block, because a Phi temporary may be live at the end of
           // the previous block, and if it is also assigned in the first
           // instruction of this block, the adjacent live ranges get merged.
-          if (static_cast<class Inst *>(&Instr) != FirstInst &&
-              !Instr.isDestRedefined() &&
+          if (&Instr != FirstInst && !Instr.isDestRedefined() &&
               Dest->getLiveRange().containsValue(InstNumber - 1, IsDest))
             Invalid = true;
           if (Invalid) {