Suppress following warning when compiling with W=1:

drivers/net/ethernet/mellanox/mlxsw//i2c.c:78: warning: Function
parameter or member 'cmd' not described in 'mlxsw_i2c'
Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Reviewed-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>