PCI: Handle case when no pci device can provide cache line size hint

Prior to this patch, if pci_read_config_byte(dev, PCI_CACHE_LINE_SIZE, ...)
returns 0 for all dev, pci_cache_line_size ends up set to zero
(instead of pci_dfl_cache_line_size).

This patch ensures the pci_cache_line_size = pci_dfl_cache_line_size
setting in the above scenario.

This happens in case of a kvm-88 guest (where, consequently, the rtl8139
NIC failed to initialize).
Acked-by: NTejun Heo <tj@kernel.org>
Signed-off-by: NCsaba Henk <csaba@gluster.com>
Signed-off-by: NJesse Barnes <jbarnes@virtuousgeek.org>

drivers/pci/quirks.c

@@ -2629,7 +2629,7 @@ static int __init pci_apply_final_quirks(void)
 	if (!pci_cache_line_size) {
 		printk(KERN_DEBUG "PCI: CLS %u bytes, default %u\n",
 		       cls << 2, pci_dfl_cache_line_size << 2);
-		pci_cache_line_size = cls;
+		pci_cache_line_size = cls ? cls : pci_dfl_cache_line_size;
 	}
 
 	return 0;