mtd: tests: fix integer overflow issues

These multiplications are done with 32-bit arithmetic, then converted to
64-bit. We should widen the integers first to prevent overflow. This
could be a problem for large (>4GB) MTD's.

Detected by Coverity.

Signed-off-by: Brian Norris <computersforpeace@gmail.com>
Cc: Akinobu Mita <akinobu.mita@gmail.com>

drivers/mtd/tests/nandbiterrs.c

@@ -364,7 +364,7 @@ static int __init mtd_nandbiterrs_init(void)
 
 	pr_info("Device uses %d subpages of %d bytes\n", subcount, subsize);
 
-	offset     = page_offset * mtd->writesize;
+	offset     = (loff_t)page_offset * mtd->writesize;
 	eraseblock = mtd_div_by_eb(offset, mtd);
 
 	pr_info("Using page=%u, offset=%llu, eraseblock=%u\n",