zink: fix synchronization when drawing from streamout

zink: fix synchronization when drawing from streamout

this was well-documented, but ultimately wrong: the synchronization
being used was for binding streamout buffers (not counter buffers) as
vertex buffers, which was already handled just fine in the normal
vertex buffer binding

drawing from streamout ONLY uses the counter buffer, which means
the counter buffer needs to be synchronized for reading

cc: mesa-stable

fixes (nv):
KHR-GL46.transform_feedback.draw_xfb_feedbackk_test
KHR-GL46.transform_feedback.draw_xfb_instanced_test
KHR-GL46.transform_feedback.draw_xfb_stream_instanced_test

Reviewed-by: Dave Airlie <airlied@redhat.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/16065>