mesa: flush and wait after creating a fallback texture

Fixes non-deterministic failures in
dEQP-EGL.functional.sharing.gles2.multithread.simple_egl_sync.images.texture_source.teximage2d_render
and others in dEQP-EGL.functional.sharing.gles2.multithread.*

Reviewed-by: Marek Olšák <marek.olsak@amd.com>
1 file changed