net: dsa: bcm_sf2: Do not override speed settings

The SF2 driver currently overrides speed settings for its port
configured using a fixed PHY, this is both unnecessary and incorrect,
because we keep feedback to the hardware parameters that we read from
the PHY device, which in the case of a fixed PHY cannot possibly change
speed.

This is a required change to allow the fixed PHY code to allow
registering a PHY with a link configured as DOWN by default and avoid
some sort of circular dependency where we require the link_update
callback to run to program the hardware, and we then utilize the fixed
PHY parameters to program the hardware with the same settings.

Fixes: 246d7f77 ("net: dsa: add Broadcom SF2 switch driver")
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>