SMOOTH_PRED: Use get_msb() to get log2 of block dimension.

Apart from being inefficient, the floating point operation log2()
was resulting in an assertion failure due to an unrelated floating
point exception that happens earlier.

Related: update the MD5s in test_intra_pred_speed to fix that failure
too.

BUG=aomedia:384

Change-Id: I18dc0733e880bac21b3d07ad874f8ae341f59f06
2 files changed