powerpc/pseries: Quieten ibm,pcie-link-speed-stats warning

The ibm,pcie-link-speed-stats isn't mandatory, so we shouldn't print
a high priority error message when missing. One example where we see
this is QEMU.

Reduce it to pr_debug.
Signed-off-by: NAnton Blanchard <anton@samba.org>
Signed-off-by: NMichael Ellerman <mpe@ellerman.id.au>

arch/powerpc/platforms/pseries/pci.c

@@ -134,7 +134,7 @@ int pseries_root_bridge_prepare(struct pci_host_bridge *bridge)
 	of_node_put(pdn);
 
 	if (rc) {
-		pr_err("no ibm,pcie-link-speed-stats property\n");
+		pr_debug("no ibm,pcie-link-speed-stats property\n");
 		return 0;
 	}