sparse-checkout: fix a couple minor memory leaks

These were introduced in commit 55dfcf9591 ("sparse-checkout: clear
tracked sparse dirs", 2021-09-08) and missed in my review at the time.
Plug the leaks.

Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/sparse-checkout.c

@@ -182,6 +182,8 @@ static void clean_tracked_sparse_directories(struct repository *r)
 				item->string);
 		}
 
+		strvec_clear(&s);
+		clear_pathspec(&p);
 		dir_clear(&dir);
 	}