selftests/bpf: Fix error checking for cpumask_success__load()

We should verify the return value of cpumask_success__load().

Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
Cc: David Vernet <void@manifault.com>

tools/testing/selftests/bpf/prog_tests/cpumask.c

@@ -27,7 +27,7 @@ static void verify_success(const char *prog_name)
 	struct bpf_program *prog;
 	struct bpf_link *link = NULL;
 	pid_t child_pid;
-	int status;
+	int status, err;
 
 	skel = cpumask_success__open();
 	if (!ASSERT_OK_PTR(skel, "cpumask_success__open"))
@@ -36,8 +36,8 @@ static void verify_success(const char *prog_name)
 	skel->bss->pid = getpid();
 	skel->bss->nr_cpus = libbpf_num_possible_cpus();
 
-	cpumask_success__load(skel);
-	if (!ASSERT_OK_PTR(skel, "cpumask_success__load"))
+	err = cpumask_success__load(skel);
+	if (!ASSERT_OK(err, "cpumask_success__load"))
 		goto cleanup;
 
 	prog = bpf_object__find_program_by_name(skel->obj, prog_name);