[Sema] Remove an unnecessary cast (NFC) (llvm#146808)

The only use of BW is to initialize BitWidth.  This patch renames BW
to BitWdith while removing the cast statement.

Author: kazutakahirata

clang/lib/Sema/SemaDeclCXX.cpp

@@ -3431,7 +3431,7 @@ static bool IsUnusedPrivateField(const FieldDecl *FD) {
 NamedDecl *
 Sema::ActOnCXXMemberDeclarator(Scope *S, AccessSpecifier AS, Declarator &D,
                                MultiTemplateParamsArg TemplateParameterLists,
-                               Expr *BW, const VirtSpecifiers &VS,
+                               Expr *BitWidth, const VirtSpecifiers &VS,
                                InClassInitStyle InitStyle) {
   const DeclSpec &DS = D.getDeclSpec();
   DeclarationNameInfo NameInfo = GetNameForDeclarator(D);
@@ -3442,8 +3442,6 @@ Sema::ActOnCXXMemberDeclarator(Scope *S, AccessSpecifier AS, Declarator &D,
   if (Loc.isInvalid())
     Loc = D.getBeginLoc();
 
-  Expr *BitWidth = static_cast<Expr*>(BW);
-
   assert(isa<CXXRecordDecl>(CurContext));
   assert(!DS.isFriendSpecified());