Recent code added in EXT_INTRA wasn't compatible with CfL,
because it assumed that the PREDICTION_MODE was the same
for luma and chroma, which is not the case with CfL.

UV_PREDICTION_MODE must be converted to PREDICTION_MODE for
av1_is_directional_mode function.

Change-Id: I10e42e3f4a904905f41205d0018f97807959e841