dm: test: Improve partition test error output

Improve the logging when the partition test fails so that it is clear
what went wrong, shown with actual values.

Signed-off-by: Joshua Watt <JPEWhacker@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/test/dm/part.c b/test/dm/part.c
index d5c58d6..7dd8bc7 100644
--- a/test/dm/part.c
+++ b/test/dm/part.c
@@ -17,10 +17,12 @@
 	struct blk_desc *mmc_dev_desc;
 	struct disk_partition part_info;
 
-	ut_asserteq(expected,
-		    part_get_info_by_dev_and_name_or_num("mmc", part_str,
-							 &mmc_dev_desc,
-							 &part_info, whole));
+	int ret = part_get_info_by_dev_and_name_or_num("mmc", part_str,
+						       &mmc_dev_desc,
+						       &part_info, whole);
+
+	ut_assertf(expected == ret, "test(%d, \"%s\", %d) == %d", expected,
+		   part_str, whole, ret);
 	return 0;
 }