gallium/radeon: fix incorrect bpe use in si_set_optimal_micro_tile_mode

Oh my god, I wonder what catastrophic issues this was causing on SI.

Cc: 13.0 <mesa-stable@lists.freedesktop.org>
Reviewed-by: Bas Nieuwenhuizen <bas@basnieuwenhuizen.nl>
Reviewed-by: Nicolai Hähnle <nicolai.haehnle@amd.com>
1 file changed