brcmfmac: remove (ab)use of NL80211_NUM_ACS

Used NL80211_NUM_ACS to indicate the BCMC fifo used in the driver
which has the same value now, but it is a bad idea relying on that.

Signed-off-by: Arend van Spriel <arend@broadcom.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>