Fix comment.

compiler/rustc_passes/src/check_attr.rs

@@ -1018,7 +1018,8 @@ impl CheckAttrVisitor<'tcx> {
         }
     }
 
-    /// Checks if `#[rustc_legacy_const_generics]` is applied to a function and has a valid argument.
+    /// Checks that the dep-graph debugging attributes are only present when the query-dep-graph
+    /// option is passed to the compiler.
     fn check_rustc_dirty_clean(&self, attr: &Attribute) -> bool {
         if self.tcx.sess.opts.debugging_opts.query_dep_graph {
             true