Fix lint description

Author: estebank

compiler/rustc_lint/src/default_could_be_derived.rs

@@ -59,9 +59,8 @@ declare_lint! {
 }
 
 declare_lint! {
-    /// The `manual_default_for_type_with_default_fields` lint checks for
-    /// manual `impl` blocks of the `Default` trait of types with default
-    /// field values.
+    /// The `default_overrides_default_fields` lint checks for manual `impl` blocks of the
+    /// `Default` trait of types with default field values.
     ///
     /// ### Example
     ///