net: mscc: ocelot: fix pMAC TX RMON stats for bucket 256-511 and above

The typo from ocelot_port_rmon_stats_cb() was also carried over to
ocelot_port_pmac_rmon_stats_cb() as well, leading to incorrect TX RMON
stats for the pMAC too.

Fixes: ab3f97a9

 ("net: mscc: ocelot: export ethtool MAC Merge stats for Felix VSC9959")
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Reviewed-by: Florian Fainelli <florian.fainelli@broadcom.com>
Link: https://lore.kernel.org/r/20231214000902.545625-2-vladimir.oltean@nxp.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>