nand_util: treat WITH_YAFFS_OOB as a mode

When specified in the flags argument of nand_write, WITH_YAFFS_OOB causes an
operation which is mutually exclusive with the 'usual' way of writing.

Add a check that client code does not specify WITH_YAFFS_OOB along with any
other flags and add a comment indicating that the WITH_YAFFS_OOB flag should
not be mixed with other flags.

Signed-off-by: Ben Gardiner <bengardiner@nanometrics.ca>
CC: Scott Wood <scottwood@freescale.com>
Signed-off-by: Scott Wood <scottwood@freescale.com>
diff --git a/drivers/mtd/nand/nand_util.c b/drivers/mtd/nand/nand_util.c
index 762ac53..e4ef858 100644
--- a/drivers/mtd/nand/nand_util.c
+++ b/drivers/mtd/nand/nand_util.c
@@ -461,6 +461,9 @@
 
 #ifdef CONFIG_CMD_NAND_YAFFS
 	if (flags & WITH_YAFFS_OOB) {
+		if (flags & ~WITH_YAFFS_OOB)
+			return -EINVAL;
+
 		int pages;
 		pages = nand->erasesize / nand->writesize;
 		blocksize = (pages * nand->oobsize) + nand->erasesize;