mtd: tests: fix more potential integer overflows

Caught by Coverity (CID #200625 and others)

Signed-off-by: Brian Norris <computersforpeace@gmail.com>
Cc: Akinobu Mita <akinobu.mita@gmail.com>
diff --git a/drivers/mtd/tests/torturetest.c b/drivers/mtd/tests/torturetest.c
index b55bc52..5045cf1 100644
--- a/drivers/mtd/tests/torturetest.c
+++ b/drivers/mtd/tests/torturetest.c
@@ -101,11 +101,11 @@
 {
 	int err, retries = 0;
 	size_t read;
-	loff_t addr = ebnum * mtd->erasesize;
+	loff_t addr = (loff_t)ebnum * mtd->erasesize;
 	size_t len = mtd->erasesize;
 
 	if (pgcnt) {
-		addr = (ebnum + 1) * mtd->erasesize - pgcnt * pgsize;
+		addr = (loff_t)(ebnum + 1) * mtd->erasesize - pgcnt * pgsize;
 		len = pgcnt * pgsize;
 	}
 
@@ -155,11 +155,11 @@
 {
 	int err;
 	size_t written;
-	loff_t addr = ebnum * mtd->erasesize;
+	loff_t addr = (loff_t)ebnum * mtd->erasesize;
 	size_t len = mtd->erasesize;
 
 	if (pgcnt) {
-		addr = (ebnum + 1) * mtd->erasesize - pgcnt * pgsize;
+		addr = (loff_t)(ebnum + 1) * mtd->erasesize - pgcnt * pgsize;
 		len = pgcnt * pgsize;
 	}
 	err = mtd_write(mtd, addr, len, &written, buf);