powerpc/eeh: Fix misleading comment in __eeh_addr_cache_get_device()

Commit "0ba17888 powerpc/eeh: Remove reference to PCI device"
removed a call to pci_dev_get() from __eeh_addr_cache_get_device() but
did not update the comment to match.

Signed-off-by: Sam Bobroff <sam.bobroff@au1.ibm.com>
Reviewed-by: Alexey Kardashevskiy <aik@ozlabs.ru>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>