Return -1 for unknown PCI bus affinity

When we don't know the node a PCI bus is connected to return -1.
This matches the generic code. 

Noticed by Ravikiran G Thirumalai <kiran@scalex86.org>

Cc: Ravikiran G Thirumalai <kiran@scalex86.org>

Signed-off-by: Andi Kleen <ak@suse.de>

Index: linux/arch/x86_64/mm/srat.c
===================================================================
--- linux.orig/arch/x86_64/mm/srat.c
+++ linux/arch/x86_64/mm/srat.c
@@ -23,15 +23,16 @@ static struct acpi_table_slit *acpi_slit
 static nodemask_t nodes_parsed __initdata;
 static nodemask_t nodes_found __initdata;
 static struct node nodes[MAX_NUMNODES] __initdata;
-static __u8  pxm2node[256] = { [0 ... 255] = 0xff };
+static u8 pxm2node[256] = { [0 ... 255] = 0xff };
 
 static int node_to_pxm(int n);
 
 int pxm_to_node(int pxm)
 {
 	if ((unsigned)pxm >= 256)
-		return 0;
-	return pxm2node[pxm];
+		return -1;
+	/* Extend 0xff to (int)-1 */
+	return (signed char)pxm2node[pxm];
 }
 
 static __init int setup_node(int pxm)