Fix encryption root hierarchy issue

After doing a recursive raw receive, zfs userspace performs
a final pass to adjust the encryption root hierarchy as
needed. Unfortunately, the FORCE_INHERIT ioctl had a bug
which caused the encryption root to always be assigned to
the direct parent instead of the inheriting parent. This
patch simply fixes this issue.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Alek Pinchuk <apinchuk@datto.com>
Signed-off-by: Tom Caputi <tcaputi@datto.com>
Closes #6847 
Closes #6848

module/zfs/dsl_crypt.c

@@ -1454,7 +1454,8 @@ spa_keystore_change_key_sync(void *arg, dmu_tx_t *tx)
 		    0, 0, NULL, tx);
 
 		rddobj = ds->ds_dir->dd_object;
-		new_rddobj = ds->ds_dir->dd_parent->dd_object;
+		VERIFY0(dsl_dir_get_encryption_root_ddobj(ds->ds_dir->dd_parent,
+		    &new_rddobj));
 	}
 
 	if (wkey == NULL) {