of: Provide default of_node_to_nid() implementation.

of_node_to_nid() is only relevant in a few architectures.  Don't force
everyone to implement it anyway.

Signed-off-by: Grant Likely <grant.likely@secretlab.ca>
diff --git a/arch/sparc/include/asm/prom.h b/arch/sparc/include/asm/prom.h
index c82a7da..291f1257 100644
--- a/arch/sparc/include/asm/prom.h
+++ b/arch/sparc/include/asm/prom.h
@@ -43,8 +43,7 @@
 extern int of_find_in_proplist(const char *list, const char *match, int len);
 #ifdef CONFIG_NUMA
 extern int of_node_to_nid(struct device_node *dp);
-#else
-#define of_node_to_nid(dp)	(-1)
+#define of_node_to_nid of_node_to_nid
 #endif
 
 extern void prom_build_devicetree(void);