net: pcs: xpcs: Convert xpcs_compat to dw_xpcs_compat

The xpcs_compat structure has been left as the only dw-prefix-less
structure since the previous commit. Let's unify at least the structures
naming in the driver by adding the dw_-prefix to it.

Signed-off-by: Serge Semin <fancer.lancer@gmail.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>