builtin-diff: fix comparison between two blobs.

The code forgot that setup_revisions() leaves parsed object
names in reverse in the list.

Signed-off-by: Junio C Hamano <junkio@cox.net>

builtin-diff.c

@@ -132,7 +132,9 @@ static int builtin_diff_blobs(struct rev_info *revs,
 			      int argc, const char **argv,
 			      struct blobinfo *blob)
 {
-	/* Blobs */
+	/* Blobs: the arguments are reversed when setup_revisions()
+	 * picked them up.
+	 */
 	unsigned mode = canon_mode(S_IFREG | 0644);
 
 	while (1 < argc) {
@@ -145,8 +147,8 @@ static int builtin_diff_blobs(struct rev_info *revs,
 	}
 	stuff_change(&revs->diffopt,
 		     mode, mode,
-		     blob[0].sha1, blob[1].sha1,
-		     blob[1].name, blob[1].name);
+		     blob[1].sha1, blob[0].sha1,
+		     blob[0].name, blob[0].name);
 	diffcore_std(&revs->diffopt);
 	diff_flush(&revs->diffopt);
 	return 0;