osbuild/mkdir: make Mode a pointer

The default value for the `os.FileMode` is zero, but the actual default
value used by the stage if no value is specified in the options is
`0777`. By using the pointer, we'll allow one to specify `0000`
permissions as a value which won't be omitted from the stage options.

Signed-off-by: Tomáš Hozza <thozza@redhat.com>

internal/manifest/commit_deployment.go

@@ -93,7 +93,7 @@ func (p *OSTreeDeployment) serialize() osbuild.Pipeline {
 		Paths: []osbuild.MkdirStagePath{
 			{
 				Path: "/boot/efi",
-				Mode: os.FileMode(0700),
+				Mode: common.ToPtr(os.FileMode(0700)),
 			},
 		},
 	}))