src/append_reader.c: print more info when it reads bad data

When append_reader gets bad data, print the actual and expected values.
This was helpful to me when hunting a failure in generic/069 on ceph
recently.

Signed-off-by: Jeff Layton <jlayton@kernel.org>
Reviewed-by: Eryu Guan <guaneryu@gmail.com>
Signed-off-by: Eryu Guan <guaneryu@gmail.com>

src/append_reader.c

@@ -34,7 +34,7 @@ int main(int argc, char **argv)
 		}
 
 		if (d != i) {
-			fprintf(stderr, "bad data, offset = %u", i * 4);
+			fprintf(stderr, "bad data, offset = %u, got %d wanted %d\n", i * 4, d, i);
 			exit(1);
 		}
 	}