net: mscc: ocelot: allow ocelot_stat_layout elements with no name

We will add support for pMAC counters and MAC merge layer counters,
which are only reported via the structured stats, and the current
ocelot_get_strings() stands in our way, because it expects that the
statistics should be placed in the data array at the same index as found
in the ocelot_stats_layout array.

That is not true. Statistics which don't have a name should not be
exported to the unstructured ethtool -S, so we need to have different
indices into the ocelot_stats_layout array (i) and into the data array
(data itself).

Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>