staging: brcm80211: allow changing channel by mac80211 when associated

When associated on 5G the driver receives a probe request for 2G with
a 2G rate specified. The driver asserts as the operating band is still
5G when the probe request packet is given. Root cause was that ioctl
function did fail upon setting the channel as requested by mac80211
when we are associated.

Signed-off-by: Arend van Spriel <arend@broadcom.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>