nand: Fix nand_erase_opts() offset check

NAND Flash is erased by blocks, not by pages.

Signed-off-by: Benoît Thébaudeau <benoit.thebaudeau@advansee.com>
Cc: Scott Wood <scottwood@freescale.com>
diff --git a/drivers/mtd/nand/nand_util.c b/drivers/mtd/nand/nand_util.c
index 3f11103..2855683 100644
--- a/drivers/mtd/nand/nand_util.c
+++ b/drivers/mtd/nand/nand_util.c
@@ -80,8 +80,8 @@
 	struct mtd_oob_ops oob_opts;
 	struct nand_chip *chip = meminfo->priv;
 
-	if ((opts->offset & (meminfo->writesize - 1)) != 0) {
-		printf("Attempt to erase non page-aligned data\n");
+	if ((opts->offset & (meminfo->erasesize - 1)) != 0) {
+		printf("Attempt to erase non block-aligned data\n");
 		return -1;
 	}