i965: fix clear color bo address relocation

Fixes: 7987d041 ("i965/surface_state: Emit the clear color address instead of value.")
Signed-off-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
(cherry picked from commit 420bf14e)