radv: Fix DCC image store check

Doesn't seem to be causing any issues right now but could with modifiers potentially.

Matches what is in RadeonSI where the comment is also shamelessly stolen from.

Signed-off-by: Joshua Ashton <joshua@froggi.es>
Reviewed-by: Bas Nieuwenhuizen <bas@basnieuwenhuizen.nl>
Part-of: <mesa/mesa!12811>
83 jobs for radv-doom-eternal-dcc-fix