iris: Handle states=NULL in iris_bind_sampler_states

Clover likes to do this to clear our a bunch of samplers without
actually passing an array of NULL pointers.  It's easy enough to
handle in iris.

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/13072>
1 file changed