net/ethernet/sfc: Don't use of_node_to_eeh_dev()

This is deprecated, it forces the driver to hop via the OF node
that may or may not exist, instead use pci_dev_to_eeh_dev() which
is simpler.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Acked-by: Shradha Shah <sshah@solarflare.com>