i965/miptree: Add a return for updating of winsys

i965/miptree: Add a return for updating of winsys

There is nothing particularly useful to do currently if the update
fails, but there is no point carrying on either. As a result, this has a
behavior change.

v2: Make the return type a bool (Topi)

v3: Don't leak the bo if update_winsys_renderbuffer fails. (Jason)

Signed-off-by: Ben Widawsky <benjamin.widawsky@intel.com>
Acked-by: Daniel Stone <daniels@collabora.com>
Reviewed-by: Topi Pohjolainen <topi.pohjolainen@intel.com> (v2)
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
Reviewed-by: Chad Versace <chadversary@chromium.org>