staging: brcm80211: consistent naming of struct net_device *ndev

Code cleanup. Various names (ndev, net, dev) were used for the
same structure. Settled for 'ndev'.

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