staging: brcm80211: got rid of several void pointers in softmac

Code cleanup. Replaced void pointers by less generic pointer types.

Reported-by: Julian Calaby <julian.calaby@gmail.com>
Reviewed-by: Pieter-Paul Giesberts <pieterpg@broadcom.com>
Signed-off-by: Arend van Spriel <arend@broadcom.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>