PCI: Delete unused extern in powermac/pci.c

This file no longer uses pci_cache_line_size, so delete the declaration

Signed-off-by: Matthew Wilcox <matthew@wil.cx>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Acked-by: Jeff Garzik <jeff@garzik.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>