[VE] Change to use isa

[kaz7]

Summary

Change to use isa instead of dyn_cast to avoid a warning.

[simoll]

I'd say you can commit a minor NFC like this one (in particular on a code base you have authored for the most part) without review.

llvm/lib/Target/VE/VEISelLowering.cpp

bool VETargetLowering::hasAndNot(SDValue Y) const {
   // function is used to check whether an immediate value is OK for and-not
   // instruction as both X and Y.  Generating additional instruction to
   // retrieve an immediate value is no good since the purpose of this
   // function is to convert a series of 3 instructions to another series of
   // 3 instructions with better parallelism.  Therefore, we return false
   // for all immediate values now.
   // FIXME: Change hasAndNot function to have two operands to make it work
   //        correctly with Aurora VE.
-  if (auto *C = dyn_cast<ConstantSDNode>(Y))
+  if (isa<ConstantSDNode>(Y))
     return false;
 
   // It's ok for generic registers.
   return true;
 }
 
 VETargetLowering::VETargetLowering(const TargetMachine &TM,
                                    const VESubtarget &STI)