samples/damon/prcl: use damon_initialized()

damon_sample_prcl 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/[e-mail]
Signed-off-by: SeongJae Park <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>

samples/damon/prcl.c

···
 	}
 }
 
-static bool init_called;
-
 static int damon_sample_prcl_enable_store(
 		const char *val, const struct kernel_param *kp)
 {
···
 	if (enabled == is_enabled)
 		return 0;
 
-	if (!init_called)
+	if (!damon_initialized())
 		return 0;
 
 	if (enabled) {
···
 {
 	int err = 0;
 
-	init_called = true;
+	if (!damon_initialized()) {
+		if (enabled)
+			enabled = false;
+		return -ENOMEM;
+	}
+
 	if (enabled) {
 		err = damon_sample_prcl_start();
 		if (err)