test: dm: restore /firmware nodes after testing

dm_test_restore() is called after dm unit test is run.
But this function does not scan any nodes under /firmware since
it calls dm_scan_fdt().

This causes an issue. For instance, scmi_sandbox_agent device
will disappear after running 'ut dm scmi_sandbox_agent'.

So call dm_extended_scan() instead. This change will be coherent
with what dm_scan() and test_pre_run() does.

Signed-off-by: AKASHI Takahiro <takahiro.akashi@linaro.org>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/test/test-main.c b/test/test-main.c
index b3c30d9..2a3b2ba 100644
--- a/test/test-main.c
+++ b/test/test-main.c
@@ -272,7 +272,7 @@
 		return ret;
 	dm_scan_plat(false);
 	if (!CONFIG_IS_ENABLED(OF_PLATDATA))
-		dm_scan_fdt(false);
+		dm_extended_scan(false);
 
 	return 0;
 }