samples/damon/prcl: avoid starting DAMON before initialization

Commit 2780505 ("samples/damon/prcl: fix boot time enable crash") is
somehow incompletely applying the origin patch [1].  It is missing the
part that avoids starting DAMON before module initialization.  Probably a
mistake during a merge has happened.  Fix it by applying the missed part
again.

Link: https://lkml.kernel.org/r/20250909022238.2989-3-sj@kernel.org
Link: https://lore.kernel.org/20250706193207.39810-3-sj@kernel.org [1]
Fixes: 2780505 ("samples/damon/prcl: fix boot time enable crash")
Signed-off-by: SeongJae Park <sj@kernel.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Author: sjp38

samples/damon/prcl.c

@@ -137,6 +137,9 @@ static int damon_sample_prcl_enable_store(
 	if (enabled == is_enabled)
 		return 0;
 
+	if (!init_called)
+		return 0;
+
 	if (enabled) {
 		err = damon_sample_prcl_start();
 		if (err)