modetest: print signed values correctly

Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.co.uk>
Reviewed-by: Emil Velikov <emil.l.velikov@gmail.com>
diff --git a/tests/modetest/modetest.c b/tests/modetest/modetest.c
index a5ac5bd..21d5438 100644
--- a/tests/modetest/modetest.c
+++ b/tests/modetest/modetest.c
@@ -314,6 +314,8 @@
 	printf("\t\tvalue:");
 	if (drm_property_type_is(prop, DRM_MODE_PROP_BLOB))
 		dump_blob(dev, value);
+	else if (drm_property_type_is(prop, DRM_MODE_PROP_SIGNED_RANGE))
+		printf(" %"PRId64"\n", value);
 	else
 		printf(" %"PRIu64"\n", value);
 }