Clarify some code based on static analysis complaints; NFC

In one case, we have a null pointer check that's unnecessary because
the only caller of the function already asserts the value is non-null.

In the other case, we've got an anti-pattern of `is` followed by `get`.
The logic was easier to repair by changing `get` to `cast`.

Neither case is a functional change.

Author: AaronBallman

clang/lib/CodeGen/CGHLSLRuntime.cpp

@@ -589,8 +589,7 @@ void CGHLSLRuntime::initializeBufferFromBinding(const HLSLBufferDecl *BufDecl,
   auto *NonUniform = llvm::ConstantInt::get(Int1Ty, false);
   auto *Index = llvm::ConstantInt::get(CGM.IntTy, 0);
   auto *RangeSize = llvm::ConstantInt::get(CGM.IntTy, 1);
-  auto *Space =
-      llvm::ConstantInt::get(CGM.IntTy, RBA ? RBA->getSpaceNumber() : 0);
+  auto *Space = llvm::ConstantInt::get(CGM.IntTy, RBA->getSpaceNumber());
   Value *Name = nullptr;
 
   llvm::Intrinsic::ID IntrinsicID =

clang/lib/Sema/SemaHLSL.cpp

@@ -2418,7 +2418,7 @@ static bool CheckFloatOrHalfRepresentation(Sema *S, SourceLocation Loc,
                                            clang::QualType PassedType) {
   clang::QualType BaseType =
       PassedType->isVectorType()
-          ? PassedType->getAs<clang::VectorType>()->getElementType()
+          ? PassedType->castAs<clang::VectorType>()->getElementType()
           : PassedType;
   if (!BaseType->isHalfType() && !BaseType->isFloat32Type())
     return S->Diag(Loc, diag::err_builtin_invalid_arg_type)