ALSA: pcmtest: Don't use static storage to track per device data

While there is probably only ever a single instance of such a pcmtst
device, it's still bad style to use a static variable to store per
device data. Make use of platform_get_drvdata() and
platform_set_drvdata() which fixes a data corruption if there should be
two or more such devices (or this driver is used as a template for
another driver).

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Acked-by: Ivan Orlov <ivan.orlov0322@gmail.com>
Link: https://lore.kernel.org/r/20230707075058.3402832-2-u.kleine-koenig@pengutronix.de
Signed-off-by: Takashi Iwai <tiwai@suse.de>

Author: Uwe Kleine-König

sound/drivers/pcmtest.c

@@ -110,8 +110,6 @@ struct pcmtst_buf_iter {
 	struct timer_list timer_instance;
 };
 
-static struct pcmtst *pcmtst;
-
 static struct snd_pcm_hardware snd_pcmtst_hw = {
 	.info = (SNDRV_PCM_INFO_INTERLEAVED |
 		 SNDRV_PCM_INFO_BLOCK_TRANSFER |
@@ -552,6 +550,7 @@ static int snd_pcmtst_create(struct snd_card *card, struct platform_device *pdev
 static int pcmtst_probe(struct platform_device *pdev)
 {
 	struct snd_card *card;
+	struct pcmtst *pcmtst;
 	int err;
 
 	err = dma_set_mask_and_coherent(&pdev->dev, DMA_BIT_MASK(32));
@@ -573,11 +572,15 @@ static int pcmtst_probe(struct platform_device *pdev)
 	if (err < 0)
 		return err;
 
+	platform_set_drvdata(pdev, pcmtst);
+
 	return 0;
 }
 
-static void pdev_remove(struct platform_device *dev)
+static void pdev_remove(struct platform_device *pdev)
 {
+	struct pcmtst *pcmtst = platform_get_drvdata(pdev);
+
 	snd_pcmtst_free(pcmtst);
 }