r600: Update the PS state when MSAA-ness changes, too.

r600: Update the PS state when MSAA-ness changes, too.

Avoids a regression when enabling shader precompilation, where the
precompile would happen with MSAA disabled (so no sample mask export) but
we'd never catch up to the shader being rendered with MSAA.

Doesn't fix any current testcases, though.

Acked-by: Gert Wollny <gert.wollny@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/14427>