[mlir][llvm] Builders dont access null attr (NFC)

[gysit]

Nice!

mlir/include/mlir/Dialect/LLVMIR/LLVMAttrDefs.td

let parameters = (ins
     OptionalParameter<"unsigned">:$line,
     OptionalParameter<"unsigned">:$column
   );
   let builders = [
     AttrBuilderWithInferredContext<(ins
       "DIScopeAttr":$scope, "DIFileAttr":$file, "unsigned":$line,
       "unsigned":$column
     ), [{
-      return $_get(file.getContext(), scope, file, line, column);
+      return $_get(scope.getContext(), scope, file, line, column);
     }]>
   ];
   let assemblyFormat = "`<` struct(params) `>`";
 }
 
 //===----------------------------------------------------------------------===//
 // DILexicalBlockFileAttr
 //===----------------------------------------------------------------------===//
 
 def LLVM_DILexicalBlockFile : LLVM_Attr<"DILexicalBlockFile", "di_lexical_block_file",
                                         /*traits=*/[], "DIScopeAttr"> {
   let parameters = (ins
     "DIScopeAttr":$scope,
     OptionalParameter<"DIFileAttr">:$file,
     "unsigned":$discriminator
   );
   let builders = [
     AttrBuilderWithInferredContext<(ins
       "DIScopeAttr":$scope, "DIFileAttr":$file, "unsigned":$discriminator
     ), [{
-      return $_get(file.getContext(), scope, file, discriminator);
+      return $_get(scope.getContext(), scope, file, discriminator);
     }]>
   ];
   let assemblyFormat = "`<` struct(params) `>`";
 }
 
 //===----------------------------------------------------------------------===//
 // DILocalVariableAttr
 //===----------------------------------------------------------------------===//
let parameters = (ins
     OptionalParameter<"DITypeAttr">:$type
   );
   let builders = [
     AttrBuilderWithInferredContext<(ins
       "DIScopeAttr":$scope, "StringRef":$name, "DIFileAttr":$file,
       "unsigned":$line, "unsigned":$arg, "unsigned":$alignInBits,
       "DITypeAttr":$type
     ), [{
-      MLIRContext *ctx = file.getContext();
+      MLIRContext *ctx = scope.getContext();
       return $_get(ctx, scope, StringAttr::get(ctx, name), file, line,
                    arg, alignInBits, type);
     }]>
   ];
   let assemblyFormat = "`<` struct(params) `>`";
 }
 
 //===----------------------------------------------------------------------===//