fix go vet failures

cache/refs.go:110::error: unreachable code (vet)
util/progress/progress.go:119::error: unreachable code (vet)
util/progress/progress_test.go:130::error: unreachable code (vet)

Signed-off-by: Akihiro Suda <suda.akihiro@lab.ntt.co.jp>

cache/refs.go

@@ -94,20 +94,17 @@ func (cr *cacheRecord) Mount() ([]mount.Mount, error) {
 			return nil, errors.Wrapf(err, "failed to mount %s", cr.id)
 		}
 		return m, nil
-	} else {
-		if cr.viewMount == nil { // TODO: handle this better
-			cr.view = generateID()
-			m, err := cr.cm.Snapshotter.View(context.TODO(), cr.view, cr.id)
-			if err != nil {
-				cr.view = ""
-				return nil, errors.Wrapf(err, "failed to mount %s", cr.id)
-			}
-			cr.viewMount = m
-		}
-		return cr.viewMount, nil
 	}
-
-	return nil, errors.New("snapshot mount not implemented")
+	if cr.viewMount == nil { // TODO: handle this better
+		cr.view = generateID()
+		m, err := cr.cm.Snapshotter.View(context.TODO(), cr.view, cr.id)
+		if err != nil {
+			cr.view = ""
+			return nil, errors.Wrapf(err, "failed to mount %s", cr.id)
+		}
+		cr.viewMount = m
+	}
+	return cr.viewMount, nil
 }
 
 func (cr *cacheRecord) ID() string {

util/progress/progress.go

@@ -116,7 +116,6 @@ func (pr *progressReader) Read(ctx context.Context) (*Progress, error) {
 			pr.cond.Wait()
 		}
 	}
-	return nil, errors.Errorf("Read not implemented")
 }
 
 func (pr *progressReader) append(pw *progressWriter) {

util/progress/progress_test.go

@@ -127,5 +127,4 @@ func saveProgress(ctx context.Context, pr ProgressReader, t *trace) error {
 		}
 		t.items = append(t.items, *p)
 	}
-	return nil
 }