inv_txfm_add_32x32: Cleanup
inv_txfm_add_32x32: Cleanup

Only DCT_DCT and IDTX types are allowed.

Change-Id: Id354ff9ebf617164e0fc8579d667ff81488712b8

GrokImageCompression/aom,GrokImageCompression/aom,GrokImageCompression/aom,GrokImageCompression/aom,GrokImageCompression/aom,GrokImageCompression/aom