staging: brcm80211: cleanup functions in nvram.c

Several function in nvram.c take a pointer value which is not
actually used. These are removed and the header file contained
some other prototypes that were not implemented. As this source
file was the only one using the header file siutils.h it has been
removed.

Cc: devel@linuxdriverproject.org
Cc: linux-wireless@vger.kernel.org
Reviewed-by: Roland Vossen <rvossen@broadcom.com>
Reviewed-by: Henry Ptasinski <henryp@broadcom.com>
Reviewed-by: Brett Rudley <brudley@broadcom.com>
Signed-off-by: Arend van Spriel <arend@broadcom.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>