staging: net: wimax: i2400m: netdev: Demote non-conformant function header

staging: net: wimax: i2400m: netdev: Demote non-conformant function header

Fixes the following W=1 kernel build warning(s):

 drivers/net/wimax/i2400m/netdev.c:583: warning: Function parameter or member 'net_dev' not described in 'i2400m_netdev_setup'

Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Inaky Perez-Gonzalez <inaky.perez-gonzalez@intel.com>
Cc: linux-wimax@intel.com
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Jakub Kicinski <kuba@kernel.org>
Cc: Yanir Lubetkin <yanirx.lubetkin@intel.com>
Cc: netdev@vger.kernel.org
Cc: devel@driverdev.osuosl.org
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Link: https://lore.kernel.org/r/20201112131959.2213841-5-lee.jones@linaro.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>