dm: pci: Add a 'fall through' comment

For this class it is intended to set up the PCI device, so add a comment to
indicate this. This avoids a coverity warning.

Reported-by: Coverity (CID: 134194)
Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Tom Rini <trini@konsulko.com>

drivers/pci/pci_auto.c

@@ -375,6 +375,7 @@ int dm_pciauto_config_device(struct udevice *dev)
 
 	case PCI_CLASS_PROCESSOR_POWERPC: /* an agent or end-point */
 		debug("PCI AutoConfig: Found PowerPC device\n");
+		/* fall through */
 
 	default:
 		dm_pciauto_setup_device(dev, 6, pci_mem, pci_prefetch, pci_io,