staging: brcm80211: remove WLC_WATCHDOG_TBTT macro

The expanded macro expression will always be false so it has been
removed.

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