radv: Only allow 16 user SGPRs for compute on GFX9+.

Apparently for compute there are only 16 instead of the 32 for the
graphics path.

Fixes dEQP-VK.binding_model.descriptorset_random.sets16.noarray.ubolimitlow.sbolimitlow.imglimitlow.noiub.comp.0

CC: <mesa-stable@lists.freedesktop.org>
Reviewed-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
(cherry picked from commit 0dd8189f15)

src/amd/vulkan/radv_nir_to_llvm.c

@@ -695,7 +695,7 @@ static void allocate_user_sgprs(struct radv_shader_context *ctx,
 	if (ctx->shader_info->info.loads_push_constants)
 		user_sgpr_count += HAVE_32BIT_POINTERS ? 1 : 2;
 
-	uint32_t available_sgprs = ctx->options->chip_class >= GFX9 ? 32 : 16;
+	uint32_t available_sgprs = ctx->options->chip_class >= GFX9 && stage != MESA_SHADER_COMPUTE ? 32 : 16;
 	uint32_t remaining_sgprs = available_sgprs - user_sgpr_count;
 	uint32_t num_desc_set =
 		util_bitcount(ctx->shader_info->info.desc_set_used_mask);