powerpc: Const-qualify Device Node Argument to DCR Resource Extent API

Add const qualifier to device_node argument for
dcr_resource_{start,len} as of_get_property also const-qualifies this
argument.

Signed-off-by: Grant Erickson <gerickson@nuovations.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>
diff --git a/arch/powerpc/include/asm/dcr.h b/arch/powerpc/include/asm/dcr.h
index d13fb68..9d6851c 100644
--- a/arch/powerpc/include/asm/dcr.h
+++ b/arch/powerpc/include/asm/dcr.h
@@ -68,9 +68,9 @@
  * additional helpers to read the DCR * base from the device-tree
  */
 struct device_node;
-extern unsigned int dcr_resource_start(struct device_node *np,
+extern unsigned int dcr_resource_start(const struct device_node *np,
 				       unsigned int index);
-extern unsigned int dcr_resource_len(struct device_node *np,
+extern unsigned int dcr_resource_len(const struct device_node *np,
 				     unsigned int index);
 #endif /* CONFIG_PPC_DCR */
 #endif /* __ASSEMBLY__ */