radv: Don't pass a TESS_EVAL shader when tesselation is not enabled.

Otherwise on pre-GFX9, if the constant layout allows both TESS_EVAL and
GEOMETRY shaders, but the PIPELINE has only GEOMETRY, it would return the
GEOMETRY shader for the TESS_EVAL shader.

This would cause the flush_constants code to emit the GEOMETRY constants
to the TESS_EVAL registers and then conclude that it did not need to set
the GEOMETRY shader registers.

Fixes: dfff9fb6f8 "radv: Handle GFX9 merged shaders in radv_flush_constants()"
CC: 18.1 <mesa-stable@lists.freedesktop.org>
Reviewed-by: Alex Smith <asmith@feralinteractive.com>
Reviewed-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
Reviewed-by: Dave Airlie <airlied@redhat.com>

src/amd/vulkan/radv_pipeline.c

@@ -1594,6 +1594,8 @@ radv_get_shader(struct radv_pipeline *pipeline,
 		if (pipeline->shaders[MESA_SHADER_GEOMETRY])
 			return pipeline->shaders[MESA_SHADER_GEOMETRY];
 	} else if (stage == MESA_SHADER_TESS_EVAL) {
+		if (!radv_pipeline_has_tess(pipeline))
+			return NULL;
 		if (pipeline->shaders[MESA_SHADER_TESS_EVAL])
 			return pipeline->shaders[MESA_SHADER_TESS_EVAL];
 		if (pipeline->shaders[MESA_SHADER_GEOMETRY])