iris: Pin surface state buffers after possibly updating the clear color

iris: Pin surface state buffers after possibly updating the clear color

On Gen8, updating the clear color will end up allocating new
SURFACE_STATE entries.  These might end up living in a different BO
than the original copies, which means that we have to pin _after_
updating the clear color, not before.

Found by inspection.

Reviewed-by: Zoltán Böszörményi <zboszor@gmail.com>
Reviewed-by: Nanley Chery <nanley.g.chery@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/9257>