[MTD] Fix do_div() type warning in mtdconcat

It expects a uint64_t; give it one.

Signed-off-by: David Woodhouse <dwmw2@infradead.org>
diff --git a/drivers/mtd/mtdconcat.c b/drivers/mtd/mtdconcat.c
index 41844ea..96be7ef 100644
--- a/drivers/mtd/mtdconcat.c
+++ b/drivers/mtd/mtdconcat.c
@@ -178,7 +178,7 @@
 
 	/* Check alignment */
 	if (mtd->writesize > 1) {
-		loff_t __to = to;
+		uint64_t __to = to;
 		if (do_div(__to, mtd->writesize) || (total_len % mtd->writesize))
 			return -EINVAL;
 	}