ASoC: pxa: fix null-pointer dereference in filter()

kasprintf() would return NULL pointer when kmalloc() fail to allocate.
Need to check the return pointer before calling strcmp().

Fixes: 7a824e21 ("ASoC: mmp: add audio dma support")
Signed-off-by: Zeng Heng <zengheng4@huawei.com>
Link: https://lore.kernel.org/r/20221114085629.1910435-1-zengheng4@huawei.comSigned-off-by: Mark Brown <broonie@kernel.org>

sound/soc/pxa/mmp-pcm.c

@@ -98,7 +98,7 @@ static bool filter(struct dma_chan *chan, void *param)
 
 	devname = kasprintf(GFP_KERNEL, "%s.%d", dma_data->dma_res->name,
 		dma_data->ssp_id);
-	if ((strcmp(dev_name(chan->device->dev), devname) == 0) &&
+	if (devname && (strcmp(dev_name(chan->device->dev), devname) == 0) &&
 		(chan->chan_id == dma_data->dma_res->start)) {
 		found = true;
 	}