i965: Properly flush in hsw_pause_transform_feedback().

i965: Properly flush in hsw_pause_transform_feedback().

Fixes a number of transform feedback tests when run with Linux 4.8,
which allows us to use the MI_LOAD_REGISTER_REG command, at which point
we started using this new broken path.

ES3-CTS.functional.transform_feedback.array_element.interleaved.lines.*
and Piglit's arb_transform_feedback2/draw-auto are both fixed by this
patch, for example.

Thanks to Chris Wilson for catching this mistake!

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=99030
Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Anuj Phogat <anuj.phogat@gmail.com>