[POWERPC] Fix dcr_unmap()

Fix a bug in dcr_unmap().

At unmap time the DCR offset need to be added instead of substracted.

Signed-off-by: Jean-Christophe Dubois <jdubois@mc.com>
Acked-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Paul Mackerras <paulus@samba.org>
diff --git a/arch/powerpc/sysdev/dcr.c b/arch/powerpc/sysdev/dcr.c
index dffeeae..1fc5819 100644
--- a/arch/powerpc/sysdev/dcr.c
+++ b/arch/powerpc/sysdev/dcr.c
@@ -129,7 +129,7 @@
 
 	if (h.token == NULL)
 		return;
-	h.token -= dcr_n * h.stride;
+	h.token += dcr_n * h.stride;
 	iounmap(h.token);
 	h.token = NULL;
 }