swrast: add dri2ConfigQueryExtension to the correct extension list

The extension should be in the list as returned by getExtensions().
Seems to have gone unnoticed since close to nobody wants to change the
vblank mode for the software driver.

Signed-off-by: Emil Velikov <emil.velikov@collabora.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>

src/mesa/drivers/dri/swrast/swrast.c

@@ -208,6 +208,7 @@ static const __DRI2rendererQueryExtension swrast_query_renderer_extension = {
 static const __DRIextension *dri_screen_extensions[] = {
     &swrastTexBufferExtension.base,
     &swrast_query_renderer_extension.base,
+    &dri2ConfigQueryExtension.base,
     &dri2NoErrorExtension.base,
     NULL
 };