[POWERPC] Fix constantness of bootwrapper arg

Fixes the constantness of the powerpc bootwrapper's console_ops.write
routine.  Allows printing of constant strings.

Signed-off-by: Geoff Levand <geoffrey.levand@am.sony.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>
diff --git a/arch/powerpc/boot/ops.h b/arch/powerpc/boot/ops.h
index 959124f..a1581b7 100644
--- a/arch/powerpc/boot/ops.h
+++ b/arch/powerpc/boot/ops.h
@@ -51,7 +51,7 @@
 /* Console operations */
 struct console_ops {
 	int	(*open)(void);
-	void	(*write)(char *buf, int len);
+	void	(*write)(const char *buf, int len);
 	void	(*edit_cmdline)(char *buf, int len);
 	void	(*close)(void);
 	void	*data;