pkg/devicemapper: disable unused and varcheck linters

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

pkg/devicemapper/devmapper.go

@@ -14,7 +14,7 @@ import (
 )
 
 // Same as DM_DEVICE_* enum values from libdevmapper.h
-// nolint: deadcode
+// nolint: deadcode,unused,varcheck
 const (
 	deviceCreate TaskType = iota
 	deviceReload