i965: Replace dri_bo_release with drm_intel_bo_unreference.

i965: Replace dri_bo_release with drm_intel_bo_unreference.

dri_bo_release is a helper function that calls drm_intel_bo_unreference
but then also sets the pointer to NULL.  This is unnecessary, since
brw_destroy_context is called from intelDestroyContext, which also frees
brw completely.

If you're still trying to access them, you've got bigger problems.

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Eric Anholt <eric@anholt.net>