cw1200: add const to hwbus_ops structures

Declare hwbus_ops structures as const as they are only passed as an
argument to the function cw1200_core_probe. This argument is of type
const. So, make these structures const.

Signed-off-by: Bhumika Goyal <bhumirks@gmail.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>