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/readtest.c

@@ -47,7 +47,7 @@ static int pgcnt;
 static int read_eraseblock_by_page(int ebnum)
 {
 	int i, ret, err = 0;
-	loff_t addr = ebnum * mtd->erasesize;
+	loff_t addr = (loff_t)ebnum * mtd->erasesize;
 	void *buf = iobuf;
 	void *oobbuf = iobuf1;