brcm80211: smac: always set channel specified by mac80211

In some situations brcmsmac is choosing a channel internally. This makes
it difficult at times to know what channel to use for enforcing
regulatory constraints, so instead always use the channel from the
mac80211 configuration.

Reviewed-by: Arend Van Spriel <arend@broadcom.com>
Reviewed-by: Pieter-Paul Giesberts <pieterpg@broadcom.com>
Signed-off-by: Seth Forshee <seth.forshee@canonical.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>