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: Anton Blanchard <anton@samba.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
diff --git a/arch/powerpc/platforms/pseries/pci.c b/arch/powerpc/platforms/pseries/pci.c
index 67e4859..fe16a50 100644
--- a/arch/powerpc/platforms/pseries/pci.c
+++ b/arch/powerpc/platforms/pseries/pci.c
@@ -134,7 +134,7 @@
 	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;
 	}