build_intra_predictors*: reduce above_data size

currently this needs to be 2x (NEED_ABOVERIGHT) the size of the largest
block (32) + 1 (for above_left). reduce the buffer size from 128 + 16
(alignment) to 64 + 16.

Change-Id: Idaca1806c7e1214e9437de24e15edc2ebf18f95d