radeonsi/nir: Only set window_space_position for vertex shaders.

By mistake, this was previously set for all shaders.
It is a vertex shader property so only makes sense to
set it for vertex shaders.

Signed-Off-By: Timur Kristóf <timur.kristof@gmail.com>
Reviewed-By: Timothy Arceri <tarceri@itsqueeze.com>
Tested-by: Dieter Nützel <Dieter@nuetzel-hh.de>

src/gallium/drivers/radeonsi/si_shader_nir.c

@@ -343,8 +343,10 @@ void si_nir_scan_shader(const struct nir_shader *nir,
 	info->properties[TGSI_PROPERTY_NEXT_SHADER] =
 		pipe_shader_type_from_mesa(nir->info.next_stage);
 
-	info->properties[TGSI_PROPERTY_VS_WINDOW_SPACE_POSITION] =
-		nir->info.vs.window_space_position;
+	if (nir->info.stage == MESA_SHADER_VERTEX) {
+		info->properties[TGSI_PROPERTY_VS_WINDOW_SPACE_POSITION] =
+			nir->info.vs.window_space_position;
+	}
 
 	if (nir->info.stage == MESA_SHADER_TESS_CTRL) {
 		info->properties[TGSI_PROPERTY_TCS_VERTICES_OUT] =