Fix return value for setting zvol threading

We must return -1 instead of ENOENT if the special zvol threading
property set function can't locate the dataset (this would typically
happen with an encypted and unmounted zvol) so that the operation
gets inserted properly into the nvlist for operations to set. This
is because we want the property to be set once the zvol is
decrypted again.

Reviewed-by: Allan Jude <allan@klarasystems.com>
Reviewed-by: Rob Norris <robn@despairlabs.com>
Reviewed-by: Ameer Hamza <ahamza@ixsystems.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Alexander Motin <mav@FreeBSD.org>
Signed-off-by: Andrew Walker <awalker@ixsystems.com>
Closes #17836

module/zfs/zvol.c

@@ -410,7 +410,7 @@ zvol_set_volthreading(const char *name, boolean_t value)
 {
 	zvol_state_t *zv = zvol_find_by_name(name, RW_NONE);
 	if (zv == NULL)
-		return (SET_ERROR(ENOENT));
+		return (-1);
 	zv->zv_threading = value;
 	mutex_exit(&zv->zv_state_lock);
 	return (0);