dump: fix check for service dentries

Without the patch all files starting with "." will be ommited.
Use of strcmp() - explicit check for "." and ".." looks clearer.

Signed-off-by: Stanislav Kinsbursky <skinsbursky@openvz.org>
Acked-by: Pavel Emelyanov <xemul@parallels.com>
Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>