mm/damon/tests/core-kunit: handle alloc failures on damon_test_split_at()

mm/damon/tests/core-kunit: handle alloc failures on damon_test_split_at()

damon_test_split_at() is assuming all dynamic memory allocation in it will
succeed.  Those are indeed likely in the real use cases since those
allocations are too small to fail, but theoretically those could fail.  In
the case, inappropriate memory access can happen.  Fix it by appropriately
cleanup pre-allocated memory and skip the execution of the remaining tests
in the failure cases.

Link: https://lkml.kernel.org/r/20251101182021.74868-6-sj@kernel.org
Fixes: 17ccae8bb5c9 ("mm/damon: add kunit tests")
Signed-off-by: SeongJae Park <sj@kernel.org>
Cc: Brendan Higgins <brendan.higgins@linux.dev>
Cc: David Gow <davidgow@google.com>
Cc: Kefeng Wang <wangkefeng.wang@huawei.com>
Cc: <stable@vger.kernel.org>	[5.15+]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>