MT#61856 media_player: use dedicated `KERNEL_IDX_NONE`

For comparison reasons. This last unrefactored condition
was missed during the refactoring here: 93c49e9c2e

Change-Id: Iee7c01e776945a34eaa87d6c0d7bba8d405395a8

daemon/media_player.c

@@ -639,7 +639,7 @@ static void media_player_kernel_player_start_now(struct media_player *mp) {
 	mp->sink.handler->out->kernel(&info.encrypt, mp->sink.sink);
 
 	unsigned int idx = kernel_start_stream_player(&info);
-	if (idx == -1)
+	if (idx == KERNEL_IDX_NONE)
 		ilog(LOG_ERR, "Failed to start kernel media player (index %i): %s", info.packet_stream_idx, strerror(errno));
 	else
 		mp->kernel_idx = idx;