fix unnecessary type cast (rust-lang#619)

Author: tgymnich

enzyme/Enzyme/Enzyme.cpp

@@ -661,7 +661,7 @@ class Enzyme : public ModulePass {
           ty = DIFFE_TYPE::DUP_ARG;
           ++i;
           Value *offset_arg = CI->getArgOperand(i);
-          if (auto cint = dyn_cast<IntegerType>(offset_arg->getType())) {
+          if (offset_arg->getType()->isIntegerTy()) {
             batchOffset[i + 1] = offset_arg;
           } else {
             EmitFailure("IllegalVectorOffset", CI->getDebugLoc(), CI,