powerpc/eeh_sysfs: Fix incorrect comment

The EEH_ATTR_SHOW() helper is used to display fields from struct eeh_dev
not struct pci_dn.

Signed-off-by: Oliver O'Halloran <oohall@gmail.com>
Reviewed-by: Sam Bobroff <sbobroff@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20190715085612.8802-3-oohall@gmail.com