[Sema] Remove an unnecessary cast (NFC) (llvm#147154)

BitWidth is already of Expr *.

Author: kazutakahirata

clang/lib/Sema/SemaDecl.cpp

@@ -18636,8 +18636,7 @@ ExprResult Sema::VerifyBitField(SourceLocation FieldLoc,
         << FieldName << FieldTy << BitWidth->getSourceRange();
     return Diag(FieldLoc, diag::err_not_integral_type_anon_bitfield)
       << FieldTy << BitWidth->getSourceRange();
-  } else if (DiagnoseUnexpandedParameterPack(const_cast<Expr *>(BitWidth),
-                                             UPPC_BitFieldWidth))
+  } else if (DiagnoseUnexpandedParameterPack(BitWidth, UPPC_BitFieldWidth))
     return ExprError();
 
   // If the bit-width is type- or value-dependent, don't try to check