staging: brcm80211: fix cast to pointer from integer

bcm_pktq_flush and related functions only ever get 0 or a pointer for
arg, so make it a pointer.

This might fix a crash on 64bit.

Signed-off-by: Clemens Noss <cnoss@gmx.de>
Acked-by: Roland Vossen <rvossen@broadcom.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>