cnss: Update bus scale request at end of unregister

Make sure change the bus scale request with none value after
driver ops are unregister to avoid the bus scale request with
other value.

CRs-Fixed: 2259434
Change-Id: I572e43a0a22d26c81e9433acf28f82c98c357256
Signed-off-by: Hardik Kantilal Patel <hkpatel@codeaurora.org>