net: lan966x: Fix configuration of the PCS

net: lan966x: Fix configuration of the PCS

When the PCS was taken out of reset, we were changing by mistake also
the speed to 100 Mbit. But in case the link was going down, the link
up routine was setting correctly the link speed. If the link was not
getting down then the speed was forced to run at 100 even if the
speed was something else.
On lan966x, to set the speed link to 1G or 2.5G a value of 1 needs to be
written in DEV_CLOCK_CFG_LINK_SPEED. This is similar to the procedure in
lan966x_port_init.

The issue was reproduced using 1000base-x sfp module using the commands:
ip link set dev eth2 up
ip link addr add 10.97.10.2/24 dev eth2
ethtool -s eth2 speed 1000 autoneg off

Fixes: d28d6d2e37d1 ("net: lan966x: add port module support")
Signed-off-by: Horatiu Vultur <horatiu.vultur@microchip.com>
Reviewed-by: Piotr Raczynski <piotr.raczynski@intel.com>
Link: https://lore.kernel.org/r/20221221093315.939133-1-horatiu.vultur@microchip.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>