mtd: mtd_oobtest: fix error return code in mtd_oobtest_init()

Fix to return a negative error code from the error handling
case instead of 0, as done elsewhere in this function.
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Zhang Xiaoxu <zhangxiaoxu5@huawei.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20210409010739.1021001-1-zhangxiaoxu5@huawei.com

drivers/mtd/tests/oobtest.c

@@ -701,6 +701,7 @@ static int __init mtd_oobtest_init(void)
 			       (long long)addr);
 			errcnt += 1;
 			if (errcnt > 1000) {
+				err = -EINVAL;
 				pr_err("error: too many errors\n");
 				goto out;
 			}