Fix highbd_iht_test with 4, 8, and 16 daala_tx.
Fix highbd_iht_test with 4, 8, and 16 daala_tx.

This change fixes a compile error when all three of --enable-daala_dct4,
 --enable-daala_dct8 and --enable-daala_dct16 are enabled at once.

Change-Id: I4942e09fb887afbda2eda6aaacec727b5cbf6f50

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