fix a HIR doc, simplify one HIR-related function call

Author: ljedrz

src/librustc/cfg/construct.rs

@@ -42,8 +42,7 @@ pub fn construct<'tcx>(tcx: TyCtxt<'tcx>, body: &hir::Body) -> CFG {
     let body_exit;
 
     // Find the tables for this body.
-    let owner_hir_id = tcx.hir().body_owner(body.id());
-    let owner_def_id = tcx.hir().local_def_id_from_hir_id(owner_hir_id);
+    let owner_def_id = tcx.hir().body_owner_def_id(body.id());
     let tables = tcx.typeck_tables_of(owner_def_id);
 
     let mut cfg_builder = CFGBuilder {

src/librustc/hir/map/mod.rs

@@ -420,7 +420,7 @@ impl<'hir> Map<'hir> {
         }
     }
 
-    /// Returns the `NodeId` that corresponds to the definition of
+    /// Returns the `HirId` that corresponds to the definition of
     /// which this is the body of, i.e., a `fn`, `const` or `static`
     /// item (possibly associated), a closure, or a `hir::AnonConst`.
     pub fn body_owner(&self, BodyId { hir_id }: BodyId) -> HirId {