openharmony-preinit.service: enable RemainAfterExit

enable RemainAfterExit to openharmony-preinit.service to prevent 
the service from getting deactivated after initialization.

Signed-off-by: Francesco Pham <francesco.pham@huawei.com>

recipes-openharmony/openharmony/files/openharmony-preinit.service

@@ -4,6 +4,7 @@ Description=OpenHarmony pre-init setup
 [Service]
 Type=oneshot
 ExecStart=/bin/sh /usr/sbin/openharmony-preinit
+RemainAfterExit=yes
 
 [Install]
 WantedBy=multi-user.target