wifi: rndis_wlan: clean up a type issue

The rndis_bss_info_update() returns type bool.  Change the NULL
returns to false.

Signed-off-by: Dan Carpenter <error27@gmail.com>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/d1f250a3-653a-497d-9c92-12dd628b7927@kili.mountain