Fix incorrect expected error in ztest

There is an occasional ztest failure that looks like ztest: attach 
(/var/tmp/zloop-run/ztest.13a 570425344, draid1-1-0 532152320, 1) 
returned 22, expected 95. This is because the value that we return 
is EINVAL, but expected_error is set incorrectly.

Change the expected_error value to match both the comment and the 
actual error value.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Paul Dagnelie <pcd@delphix.com>
Closes #15295

cmd/ztest.c

@@ -3767,7 +3767,7 @@ ztest_vdev_attach_detach(ztest_ds_t *zd, uint64_t id)
 	else if (ashift > oldvd->vdev_top->vdev_ashift)
 		expected_error = EDOM;
 	else if (newvd_is_dspare && pvd != vdev_draid_spare_get_parent(newvd))
-		expected_error = ENOTSUP;
+		expected_error = EINVAL;
 	else
 		expected_error = 0;