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/pagetest.c

@@ -52,7 +52,7 @@ static struct rnd_state rnd_state;
 
 static int write_eraseblock(int ebnum)
 {
-	loff_t addr = ebnum * mtd->erasesize;
+	loff_t addr = (loff_t)ebnum * mtd->erasesize;
 
 	prandom_bytes_state(&rnd_state, writebuf, mtd->erasesize);
 	cond_resched();
@@ -64,7 +64,7 @@ static int verify_eraseblock(int ebnum)
 	uint32_t j;
 	int err = 0, i;
 	loff_t addr0, addrn;
-	loff_t addr = ebnum * mtd->erasesize;
+	loff_t addr = (loff_t)ebnum * mtd->erasesize;
 
 	addr0 = 0;
 	for (i = 0; i < ebcnt && bbt[i]; ++i)