devmapper: Fix gofmt related build failures

My pull request failed the build due to gofmat issues. I have run gofmt
on specified files and this commit fixes it.

Signed-off-by: Vivek Goyal <vgoyal@redhat.com>

daemon/graphdriver/devmapper/deviceset.go

@@ -62,25 +62,25 @@ type MetaData struct {
 }
 
 type DeviceSet struct {
-	MetaData		`json:"-"`
-	sync.Mutex       	`json:"-"` // Protects Devices map and serializes calls into libdevmapper
-	root             string	`json:"-"`
-	devicePrefix     string	`json:"-"`
-	TransactionId    uint64	`json:"-"`
-	NewTransactionId uint64 `json:"-"`
-	NextDeviceId     int	`json:"next_device_id"`
+	MetaData         `json:"-"`
+	sync.Mutex       `json:"-"` // Protects Devices map and serializes calls into libdevmapper
+	root             string     `json:"-"`
+	devicePrefix     string     `json:"-"`
+	TransactionId    uint64     `json:"-"`
+	NewTransactionId uint64     `json:"-"`
+	NextDeviceId     int        `json:"next_device_id"`
 
 	// Options
-	dataLoopbackSize     int64	`json:"-"`
-	metaDataLoopbackSize int64	`json:"-"`
-	baseFsSize           uint64	`json:"-"`
-	filesystem           string	`json:"-"`
-	mountOptions         string	`json:"-"`
-	mkfsArgs             []string	`json:"-"`
-	dataDevice           string	`json:"-"`
-	metadataDevice       string	`json:"-"`
-	doBlkDiscard         bool	`json:"-"`
-	thinpBlockSize       uint32	`json:"-"`
+	dataLoopbackSize     int64    `json:"-"`
+	metaDataLoopbackSize int64    `json:"-"`
+	baseFsSize           uint64   `json:"-"`
+	filesystem           string   `json:"-"`
+	mountOptions         string   `json:"-"`
+	mkfsArgs             []string `json:"-"`
+	dataDevice           string   `json:"-"`
+	metadataDevice       string   `json:"-"`
+	doBlkDiscard         bool     `json:"-"`
+	thinpBlockSize       uint32   `json:"-"`
 }
 
 type DiskUsage struct {