You can get rid of the mipmaps, if you open your button and save it as dds file again (save as, not just save), but taking care to disable mipmaps in the dialog that pops up during the saving process. If you use GIMP, you can't miss the dialog and the mipmaps, but your file shouldn't contain an alpha channel as GIMP obviously has trouble opening dds files with alpha channel. Alternatively, you should be able to do the same with Photoshop or dds converter.