net: mscc: ocelot: remove buggy and useless write to ANA_PFC_PFC_CFG

A useless write to ANA_PFC_PFC_CFG was left in while refactoring ocelot to
phylink. Since priority flow control is disabled, writing the speed has no
effect.

Further, it was using ethtool.h SPEED_ instead of OCELOT_SPEED_ macros,
which are incorrectly offset for GENMASK.

Lastly, for priority flow control to properly function, some scenarios
would rely on the rate adaptation from the PCS while the MAC speed would
be fixed. So it isn't used, and even if it was, neither "speed" nor
"mac_speed" are necessarily the correct values to be used.

Fixes: e6e12df6 ("net: mscc: ocelot: convert to phylink")
Signed-off-by: Colin Foster <colin.foster@in-advantage.com>
Reviewed-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>