block: use kstrtoul in flag_store

Use the text to integer helper that has error handling and doesn't modify
the input pointer.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Keith Busch <kbusch@kernel.org>
Reviewed-by: Chaitanya Kulkarni <kch@nvidia.com>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Reviewed-by: Kanchan Joshi <joshi.k@samsung.com>
Link: https://lore.kernel.org/r/20240613084839.1044015-9-hch@lst.de
Signed-off-by: Jens Axboe <axboe@kernel.dk>

Author: Christoph Hellwig

block/blk-integrity.c

@@ -247,8 +247,12 @@ static ssize_t flag_store(struct device *dev, struct device_attribute *attr,
 		const char *page, size_t count, unsigned char flag)
 {
 	struct blk_integrity *bi = dev_to_bi(dev);
-	char *p = (char *) page;
-	unsigned long val = simple_strtoul(p, &p, 10);
+	unsigned long val;
+	int err;
+
+	err = kstrtoul(page, 10, &val);
+	if (err)
+		return err;
 
 	if (val)
 		bi->flags |= flag;