test: Move dm_scan_plat() to test_pre_run()

Move this step over to the pre-run function.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/test/test-main.c b/test/test-main.c
index bd2f08a..fe96d73 100644
--- a/test/test-main.c
+++ b/test/test-main.c
@@ -34,6 +34,9 @@
 	if (!(test->flags & UT_TESTF_DM))
 		uts->start = mallinfo();
 
+	if (test->flags & UT_TESTF_SCAN_PDATA)
+		ut_assertok(dm_scan_plat(false));
+
 	if (test->flags & UT_TESTF_PROBE_TEST)
 		ut_assertok(do_autoprobe(uts));