Silence static analyzer getAs<VectorType> null dereference warnings. NFCI.

The static analyzer is warning about potential null dereferences, but in these cases we should be able to use castAs<VectorType> directly and if not assert will fire for us.

llvm-svn: 373478
diff --git a/clang/lib/CodeGen/CGAtomic.cpp b/clang/lib/CodeGen/CGAtomic.cpp
index a95cd12c..f9915a1 100644
--- a/clang/lib/CodeGen/CGAtomic.cpp
+++ b/clang/lib/CodeGen/CGAtomic.cpp
@@ -107,7 +107,7 @@
         }
         AtomicAlign = ValueAlign = lvalue.getAlignment();
       } else if (lvalue.isVectorElt()) {
-        ValueTy = lvalue.getType()->getAs<VectorType>()->getElementType();
+        ValueTy = lvalue.getType()->castAs<VectorType>()->getElementType();
         ValueSizeInBits = C.getTypeSize(ValueTy);
         AtomicTy = lvalue.getType();
         AtomicSizeInBits = C.getTypeSize(AtomicTy);