Use io.SeekStart instead of os.SEEK_SET

Fixes linter warnings like this one:

> distribution/pull_v2.go:229:39: SA1019: os.SEEK_SET is deprecated: Use io.SeekStart, io.SeekCurrent, and io.SeekEnd.  (staticcheck)

Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>

distribution/pull_v2.go

@@ -200,7 +200,7 @@ func (ld *v2LayerDescriptor) Download(ctx context.Context, progressOutput progre
 	}
 
 	if offset != 0 {
-		_, err := layerDownload.Seek(offset, os.SEEK_SET)
+		_, err := layerDownload.Seek(offset, io.SeekStart)
 		if err != nil {
 			if err := ld.truncateDownloadFile(); err != nil {
 				return nil, 0, xfer.DoNotRetry{Err: err}
@@ -226,7 +226,7 @@ func (ld *v2LayerDescriptor) Download(ctx context.Context, progressOutput progre
 		// Restore the seek offset either at the beginning of the
 		// stream, or just after the last byte we have from previous
 		// attempts.
-		_, err = layerDownload.Seek(offset, os.SEEK_SET)
+		_, err = layerDownload.Seek(offset, io.SeekStart)
 		if err != nil {
 			return nil, 0, err
 		}
@@ -272,7 +272,7 @@ func (ld *v2LayerDescriptor) Download(ctx context.Context, progressOutput progre
 
 	logrus.Debugf("Downloaded %s to tempfile %s", ld.ID(), tmpFile.Name())
 
-	_, err = tmpFile.Seek(0, os.SEEK_SET)
+	_, err = tmpFile.Seek(0, io.SeekStart)
 	if err != nil {
 		tmpFile.Close()
 		if err := os.Remove(tmpFile.Name()); err != nil {
@@ -310,7 +310,7 @@ func (ld *v2LayerDescriptor) truncateDownloadFile() error {
 	// Need a new hash context since we will be redoing the download
 	ld.verifier = nil
 
-	if _, err := ld.tmpFile.Seek(0, os.SEEK_SET); err != nil {
+	if _, err := ld.tmpFile.Seek(0, io.SeekStart); err != nil {
 		logrus.Errorf("error seeking to beginning of download file: %v", err)
 		return err
 	}

distribution/pull_v2_windows.go

@@ -4,8 +4,8 @@ import (
 	"context"
 	"errors"
 	"fmt"
+	"io"
 	"net/http"
-	"os"
 	"runtime"
 	"sort"
 	"strconv"
@@ -41,7 +41,7 @@ func (ld *v2LayerDescriptor) open(ctx context.Context) (distribution.ReadSeekClo
 	// We're done if the registry has this blob.
 	if err == nil {
 		// Seek does an HTTP GET.  If it succeeds, the blob really is accessible.
-		if _, err = rsc.Seek(0, os.SEEK_SET); err == nil {
+		if _, err = rsc.Seek(0, io.SeekStart); err == nil {
 			return rsc, nil
 		}
 		rsc.Close()
@@ -53,7 +53,7 @@ func (ld *v2LayerDescriptor) open(ctx context.Context) (distribution.ReadSeekClo
 		rsc = transport.NewHTTPReadSeeker(http.DefaultClient, url, nil)
 
 		// Seek does an HTTP GET.  If it succeeds, the blob really is accessible.
-		_, err = rsc.Seek(0, os.SEEK_SET)
+		_, err = rsc.Seek(0, io.SeekStart)
 		if err == nil {
 			break
 		}

integration-cli/docker_cli_daemon_test.go

@@ -2217,7 +2217,7 @@ func (s *DockerDaemonSuite) TestDaemonDiscoveryBackendConfigReload(c *testing.T)
 
 	err = configFile.Truncate(0)
 	assert.NilError(c, err)
-	_, err = configFile.Seek(0, os.SEEK_SET)
+	_, err = configFile.Seek(0, io.SeekStart)
 	assert.NilError(c, err)
 
 	_, err = configFile.Write([]byte(daemonConfig))