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

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

llvm-svn: 373584
diff --git a/clang/lib/Sema/SemaExprMember.cpp b/clang/lib/Sema/SemaExprMember.cpp
index e85499c..87114a0 100644
--- a/clang/lib/Sema/SemaExprMember.cpp
+++ b/clang/lib/Sema/SemaExprMember.cpp
@@ -1006,7 +1006,7 @@
     // Rederive where we looked up.
     DeclContext *DC = (SS.isSet()
                        ? computeDeclContext(SS, false)
-                       : BaseType->getAs<RecordType>()->getDecl());
+                       : BaseType->castAs<RecordType>()->getDecl());
 
     if (ExtraArgs) {
       ExprResult RetryExpr;