Disown dataset in zfs_sb_create()

Fix an unlikely failure cause in zfs_sb_create() which could
leave the dataset owned on error and thus unavailable until
after a reboot.  Disown the dataset if SA are expected but
are in fact missing.

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>

module/zfs/zfs_vfsops.c

@@ -646,7 +646,7 @@ zfs_sb_create(const char *osname, zfs_sb_t **zsbp)
 		error = zap_lookup(os, MASTER_NODE_OBJ, ZFS_SA_ATTRS, 8, 1,
 		    &sa_obj);
 		if (error)
-			return (error);
+			goto out;
 	} else {
 		/*
 		 * Pre SA versions file systems should never touch