mlxsw: spectrum: Allow lane to start from non-zero index

So far, the lane index always started from zero. That is not true for
modular systems with gearbox-equipped linecards. Loose the check so the
lanes can start from non-zero index.

Signed-off-by: Jiri Pirko <jiri@nvidia.com>
Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>