Correct number of records checked in show in the message to user after checked in success

If we look at the checkin method in JModelAdmin, we can see that it returns the correct number of checked in record (via $count variable) when check in success. In some special case, this number might be different with the number of $ids pass to the method. So we need to replace count($ids) with $return to show the correct number of checked in records to users.