staging: brcm80211: only enable brcmsmac if bcma is not set

brcmsmac doesn't yet use bcma, but both drivers attempt to claim the same
device.  For now, turn of brcmsmac if bcma is enabled.

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