nv50/ir/nir: set numBarriers if we emit an OP_BAR

nv50/ir/nir: set numBarriers if we emit an OP_BAR

Even though the field is called `numBarriers` we set it to 1 just like
we do with TGSI. It's unknown on what's the proper behavior here is. But
without this set the GPU will complain to us loudly, so this silences at
least that.

Fixes: a2d7a4f9788 ("nv50/ir: convert to scoped_barrier")
Signed-off-by: Karol Herbst <git@karolherbst.de>
Reviewed-by: M Henning <drawoc@darkrefraction.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/23749>