samples/damon/mtier: use damon_initialized()

damon_sample_mtier is assuming DAMON is ready to use in module_init time,
and uses its own hack to see if it is the time.  Use damon_initialized(),
which is a way for seeing if DAMON is ready to be used that is more
reliable and better to maintain instead of the hack.

Link: https://lkml.kernel.org/r/20250916033511.116366-8-sj@kernel.org
Signed-off-by: SeongJae Park <sj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

samples/damon/mtier.c

@@ -193,8 +193,6 @@ static void damon_sample_mtier_stop(void)
 	damon_destroy_ctx(ctxs[1]);
 }
 
-static bool init_called;
-
 static int damon_sample_mtier_enable_store(
 		const char *val, const struct kernel_param *kp)
 {
@@ -208,7 +206,7 @@ static int damon_sample_mtier_enable_store(
 	if (enabled == is_enabled)
 		return 0;
 
-	if (!init_called)
+	if (!damon_initialized())
 		return 0;
 
 	if (enabled) {
@@ -225,7 +223,12 @@ static int __init damon_sample_mtier_init(void)
 {
 	int err = 0;
 
-	init_called = true;
+	if (!damon_initialized()) {
+		if (enabled)
+			enabled = false;
+		return -ENOMEM;
+	}
+
 	if (enabled) {
 		err = damon_sample_mtier_start();
 		if (err)