mxc nand: use resource_size()

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
diff --git a/drivers/mtd/nand/mxc_nand.c b/drivers/mtd/nand/mxc_nand.c
index 1ffb854..8fcb33d 100644
--- a/drivers/mtd/nand/mxc_nand.c
+++ b/drivers/mtd/nand/mxc_nand.c
@@ -865,7 +865,7 @@
 		goto eres;
 	}
 
-	host->regs = ioremap(res->start, res->end - res->start + 1);
+	host->regs = ioremap(res->start, resource_size(res));
 	if (!host->regs) {
 		err = -ENOMEM;
 		goto eres;