mtd: fix possible integer overflow in erase_xfer()

The expression '1 << EraseUnitSize' is evaluated in int, which causes
a negative result when shifting by 31 - the upper bound of the valid
range [10, 31], enforced by scan_header(). This leads to incorrect
extension when storing the result in 'erase->len' (uint64_t), producing
a large unexpected value.

Found by Linux Verification Center (linuxtesting.org) with Svace.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Signed-off-by: Ivan Stepchenko <sid@itb.spb.ru>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>

Author: Ivan Stepchenko

drivers/mtd/ftl.c

@@ -344,7 +344,7 @@ static int erase_xfer(partition_t *part,
             return -ENOMEM;
 
     erase->addr = xfer->Offset;
-    erase->len = 1 << part->header.EraseUnitSize;
+    erase->len = 1ULL << part->header.EraseUnitSize;
 
     ret = mtd_erase(part->mbd.mtd, erase);
     if (!ret) {