intel/isl: Fix HiZ+CCS comment about ambiguates
Motivated by: #3788 (comment 793600)
Note that CCS isn't ambiguated during a HiZ ambiguate. Dumping the CCS surface after a HiZ ambiguate shows that the CCS is unchanged.
Fixes: 98dc7f56 ("intel/isl: Add a separate ISL_AUX_USAGE_HIZ_CCS_WT")