nv50,nvc0: Fix gallium nine regression regarding sampler bindings

The new approach is that samplers don't get unbound even if they won't be used
in a draw and we should just leave them be as well.

Fixes a regression in multiple windows games using gallium nine and nouveau.

v2: adjust num_samplers to keep track of the highest sampler bound
v3: rework how to set the new value of num_samplers

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=106577


Fixes: 4d6fab24
       "cso: don't track the number of sampler states bound"
Signed-off-by: Karol Herbst <kherbst@redhat.com>
Reviewed-by: Ilia Mirkin <imirkin@alum.mit.edu>
(cherry picked from commit fc0139d2)