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

@@ -94,7 +94,7 @@ 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)
@@ -107,9 +107,6 @@ func (cr *cacheRecord) Mount() ([]mount.Mount, error) {
 	return cr.viewMount, nil
 }
 
-	return nil, errors.New("snapshot mount not implemented")
-}
-
 func (cr *cacheRecord) ID() string {
 	return cr.id
 }

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
 }