cso: fix sampler view count in cso_set_sampler_views()

cso: fix sampler view count in cso_set_sampler_views()

We want to call pipe->set_sampler_views() with count being the
maximum of the old number of sampler views and the new number.
This makes sure we null-out any old sampler views.

We already do the same thing for sampler states in single_sampler_done().
Fixes some assertions seen in the VMware driver with XA tracker.

Cc: "10.0" "10.1" <mesa-stable@lists.freedesktop.org>
Reviewed-by: Thomas Hellstrom <thellstrom@vmware.com>
Tested-by: Thomas Hellstrom <thellstrom@vmware.com>
Reviewed-by: Roland Scheidegger <sroland@vmware.com>