staging: brcm80211: rename function variables

The fullmac driver uses dhd as variable name for the driver instance
in a number of functions. This has been changed to a more generic name
as the dhd is not meaningful (broadcom internal name).
Signed-off-by: Arend van Spriel <arend@broadcom.com>
Reviewed-by: Roland Vossen <rvossen@broadcom.com>
Reviewed-by: Franky Lin <frankyl@broadcom.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>