samples/damon: fix damon sample wsse for start failure

The damon_sample_wsse_start() can fail so we must reset the "enable"
parameter to "false" again for proper rollback.

In such cases, setting Y to "enable" then N triggers the similar crash
with wsse because damon sample start failed but the "enable" stays as Y.

Link: https://lkml.kernel.org/r/20250702000205.1921-3-honggyu.kim@sk.com
Fixes: b757c6c ("samples/damon/wsse: start and stop DAMON as the user requests")
Signed-off-by: Honggyu Kim <honggyu.kim@sk.com>
Reviewed-by: SeongJae Park <sj@kernel.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Author: honggyukim

samples/damon/wsse.c

@@ -102,8 +102,12 @@ static int damon_sample_wsse_enable_store(
 	if (enable == enabled)
 		return 0;
 
-	if (enable)
-		return damon_sample_wsse_start();
+	if (enable) {
+		err = damon_sample_wsse_start();
+		if (err)
+			enable = false;
+		return err;
+	}
 	damon_sample_wsse_stop();
 	return 0;
 }