Eliminate another compiler warning on ppc64:

  CC      drivers/md/dm-io.o
drivers/md/dm-io.c: In function `vm_dp_init':
drivers/md/dm-io.c:441: warning: cast from pointer to integer of different size

--- diff/drivers/md/dm-io.c	2004-04-06 15:55:04.655677664 +0100
+++ source/drivers/md/dm-io.c	2004-04-06 15:55:06.504396616 +0100
@@ -438,7 +438,7 @@ void vm_dp_init(struct dpages *dp, void 
 {
 	dp->get_page = vm_get_page;
 	dp->next_page = vm_next_page;
-	dp->context_u = ((unsigned) data) & (PAGE_SIZE - 1);
+	dp->context_u = ((unsigned long) data) & (PAGE_SIZE - 1);
 	dp->context_ptr = data;
 }