wl1271: Fix channel changing code

The channel changing code would a) change the BSSID to a dummy on upon
channel change, breaking connectivity, and b) not update the channel number
at all for ad-hoc, breaking adhoc.

Signed-off-by: Juuso Oikarinen <juuso.oikarinen@nokia.com>
Reviewed-by: Luciano Coelho <luciano.coelho@nokia.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>