mtd: partitions: redboot: Added conversion of operands to a larger type

The value of an arithmetic expression directory * master->erasesize is
subject to overflow due to a failure to cast operands to a larger data
type before perfroming arithmetic

Found by Linux Verification Center (linuxtesting.org) with SVACE.
Signed-off-by: Denis Arefev <arefev@swemel.ru>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20240315093758.20790-1-arefev@swemel.ru

drivers/mtd/parsers/redboot.c

@@ -102,7 +102,7 @@ static int parse_redboot_partitions(struct mtd_info *master,
 			offset -= master->erasesize;
 		}
 	} else {
-		offset = directory * master->erasesize;
+		offset = (unsigned long) directory * master->erasesize;
 		while (mtd_block_isbad(master, offset)) {
 			offset += master->erasesize;
 			if (offset == master->size)