staging: brcm80211: removed band related global vars from softmac

staging: brcm80211: removed band related global vars from softmac

Global variables are undesirable unless they are read only. Variables are
now maintained in a device specific structure.

Reported-by: Johannes Berg <johannes@sipsolutions.net>
Reviewed-by: Pieter-Paul Giesberts <pieterpg@broadcom.com>
Reviewed-by: Arend van Spriel <arend@broadcom.com>
Signed-off-by: Franky Lin <frankyl@broadcom.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>