st/mesa: use pipe_sampler_view_release for releasing sampler views

This fixes a crash when exiting Firefox. I have really no idea how Firefox
does it. It seems to involve multiple contexts and multithreading.

v2: added an XXX comment

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=81680

Acked by Christian König.
Cc: 10.2 10.3 <mesa-stable@lists.freedesktop.org>
Tested-by: Benjamin Bellec <b.bellec@gmail.com>
6 files changed