radv/gfx10: fix required subgroup size with VK_EXT_subgroup_size_control

radv/gfx10: fix required subgroup size with VK_EXT_subgroup_size_control

If compute shaders require a specific subgroup size (ie. Wave32),
we have to return the correct one.

Fixes dEQP-VK.subgroups.size_control.compute.required_subgroup_size_*.

Fixes: fb07fd4e6cb ("radv: implement VK_EXT_subgroup_size_control")
Signed-off-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
Reviewed-by: Bas Nieuwenhuizen <bas@basnieuwenhuizen.nl>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4215>