[POWERPC] Compile fixes for arch/powerpc dcr code

The new dcr code does not currently compile when configured for native
DCR access on ARCH=powerpc.  This patch fixes the problems.

Signed-off-by: David Gibson <dwg@au1.ibm.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>
diff --git a/include/asm-powerpc/dcr.h b/include/asm-powerpc/dcr.h
index b66c5e6..9338d50 100644
--- a/include/asm-powerpc/dcr.h
+++ b/include/asm-powerpc/dcr.h
@@ -33,6 +33,7 @@
  * base from the device-tree
  */
 #ifdef CONFIG_PPC_MERGE
+struct device_node;
 extern unsigned int dcr_resource_start(struct device_node *np,
 				       unsigned int index);
 extern unsigned int dcr_resource_len(struct device_node *np,