bcachefs: Use array_size() in call to copy_from_user()

Use array_size() helper, instead of the open-coded version in
call to copy_from_user().
Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

fs/bcachefs/chardev.c

@@ -360,7 +360,8 @@ static long bch2_ioctl_fsck_offline(struct bch_ioctl_fsck_offline __user *user_a
 	init_waitqueue_head(&thr->output.wait);
 	darray_init(&thr->output2);
 
-	if (copy_from_user(devs, &user_arg->devs[0], sizeof(user_arg->devs[0]) * arg.nr_devs)) {
+	if (copy_from_user(devs, &user_arg->devs[0],
+			   array_size(sizeof(user_arg->devs[0]), arg.nr_devs))) {
 		ret = -EINVAL;
 		goto err;
 	}