staging: brcm80211: simplification of brcmf_netdev_ioctl_priv()

This function is only called from within the driver. Because of that
certain simplifications (not required to lock down user mem pages,
not required to check user permissions) could be performed.

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