When chroma_sub8x8 is enable the custom DC_PRED implemented in CfL uses
chroma_up_available and chroma_left_available instead of up_available
and left_available.

It was mentioned in 3da18d60 that
this fixes a rare enc/dec mismatch issue.

Change-Id: Ie8920e956962846db15e24bcf7e7eaa13ccb8c12