ixgbe/base: fix X550em UniPHY link configuration

ixgbe/base: fix X550em UniPHY link configuration

In UniPHY we have 2 IOSF targets that are UniPHY related. We can
write to PHY and PCS. In earlier times I've been told that there
were 2 separate PCS targets for IOSF commands and that's why I
implemented it with 2 defines and adding hw->bus.lan_id, but lately
I confirmed with HW that FW takes care of which PCS "slice" we are
talking to and is directing writes to correct one, so KX4_PCS1
target is dead now and we cannot use it.

Signed-off-by: Wenzhuo Lu <wenzhuo.lu@intel.com>
Acked-by: Helin Zhang <helin.zhang@intel.com>