mtd: Add WARN_ON_ONCE() to mtd_read() to check the return value

If the driver cannot read all the requested data, -EBADMSG or
-EUCLEAN should never be returned.

Add a WARN_ON_ONCE() to help driver developers detect this error.
Signed-off-by: ZhaoLong Wang <wangzhaolong1@huawei.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20230926065733.3240322-1-wangzhaolong1@huawei.com

drivers/mtd/mtdcore.c

@@ -1505,6 +1505,8 @@ int mtd_read(struct mtd_info *mtd, loff_t from, size_t len, size_t *retlen,
 	ret = mtd_read_oob(mtd, from, &ops);
 	*retlen = ops.retlen;
 
+	WARN_ON_ONCE(*retlen != len && mtd_is_bitflip_or_eccerr(ret));
+
 	return ret;
 }
 EXPORT_SYMBOL_GPL(mtd_read);