brcmfmac: don't preset all channels as disabled

During init we take care of regulatory stuff by disabling all
unavailable channels (see brcmf_construct_chaninfo) so this predisabling
them is not really required (and this patch won't change any behavior).
It will on the other hand allow more detailed runtime control over
channels which is the main reason for this change.

Signed-off-by: Rafał Miłecki <rafal@milecki.pl>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>