i965: Replace the global brw->query.bo variable with query->bo.

i965: Replace the global brw->query.bo variable with query->bo.

Again, eliminating a global variable in favor of a per-query object
variable will help in a future where we have more queries in hardware.

Personally, I find this clearer: there's just the query object's BO,
rather than two variables that usually shadow each other.

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>