[DebugInfo] Don't dereference a dyn_cast<PDBSymbolData> result. NFCI.

The static analyzer is warning about a potential null dereference - but as we're in DataMemberLayoutItem we should be able to guarantee that the Symbol is a PDBSymbolData type, allowing us to use cast<PDBSymbolData> - and if not assert will fire for us.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@371933 91177308-0d34-0410-b5e6-96231b3b80d8

lib/DebugInfo/PDB/UDTLayout.cpp

@@ -84,7 +84,7 @@ VBPtrLayoutItem::VBPtrLayoutItem(const UDTLayoutBase &Parent,
 }
 
 const PDBSymbolData &DataMemberLayoutItem::getDataMember() {
-  return *dyn_cast<PDBSymbolData>(Symbol);
+  return *cast<PDBSymbolData>(Symbol);
 }
 
 bool DataMemberLayoutItem::hasUDTLayout() const { return UdtLayout != nullptr; }