mount: remove leading double slash

As mnt_roots always has a slash at the beginning we don't need another:

(00.156035)      1: mnt: Move the root to //tmp/.criu.mntns.ZKVJHl/15-0000000000
Signed-off-by: Pavel Tikhomirov <ptikhomirov@virtuozzo.com>
Signed-off-by: Andrei Vagin <avagin@virtuozzo.com>

criu/mount.c

@@ -3359,8 +3359,7 @@ int prepare_mnt_ns(void)
 		}
 
 		/* Set its root */
-		path[0] = '/';
-		print_ns_root(nsid, 0, path + 1, sizeof(path) - 1);
+		print_ns_root(nsid, 0, path, sizeof(path) - 1);
 		if (cr_pivot_root(path))
 			goto err;