[Hexagon] Remove a redundant cast (NFC) (llvm#165654)

*getInstrInfo() is already of type const HexagonInstrInfo &.

Author: kazutakahirata

llvm/lib/Target/Hexagon/HexagonSubtarget.cpp

@@ -544,7 +544,7 @@ int HexagonSubtarget::updateLatency(MachineInstr &SrcInst,
   if (!hasV60Ops())
     return Latency;
 
-  auto &QII = static_cast<const HexagonInstrInfo &>(*getInstrInfo());
+  const HexagonInstrInfo &QII = *getInstrInfo();
   // BSB scheduling.
   if (QII.isHVXVec(SrcInst) || useBSBScheduling())
     Latency = (Latency + 1) >> 1;