st/mesa: stop using pipe_sampler_view_release()

st/mesa: stop using pipe_sampler_view_release()

In all instances here we can replace pipe_sampler_view_release(pipe,
view) with pipe_sampler_view_reference(view, NULL) because the views
in question are private to the state tracker context.  So there's no
danger of freeing a sampler view with the wrong context.

Testing done: google chrome, misc GL demos, games

Reviewed-by: Roland Scheidegger <sroland@vmware.com>
Reviewed-by: Neha Bhende <bhenden@vmware.com>
Reviewed-by: Mathias Fröhlich <Mathias.Froehlich@web.de>
Reviewed-By: Jose Fonseca <jfonseca@vmware.com>