ALSA: n64: Fix return value check in n64audio_probe()

In case of error, the function devm_platform_ioremap_resource()
returns ERR_PTR() and never returns NULL. The NULL test in the
return value check should be replaced with IS_ERR().

Fixes: 1448f8ac ("sound: Add n64 driver")
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Reviewed-by: Lauri Kasanen <cand@gmx.com>
Link: https://lore.kernel.org/r/20210224013803.2146953-1-weiyongjun1@huawei.comSigned-off-by: Takashi Iwai <tiwai@suse.de>

sound/mips/snd-n64.c

@@ -312,14 +312,14 @@ static int __init n64audio_probe(struct platform_device *pdev)
 	}
 
 	priv->mi_reg_base = devm_platform_ioremap_resource(pdev, 0);
-	if (!priv->mi_reg_base) {
-		err = -EINVAL;
+	if (IS_ERR(priv->mi_reg_base)) {
+		err = PTR_ERR(priv->mi_reg_base);
 		goto fail_dma_alloc;
 	}
 
 	priv->ai_reg_base = devm_platform_ioremap_resource(pdev, 1);
-	if (!priv->ai_reg_base) {
-		err = -EINVAL;
+	if (IS_ERR(priv->ai_reg_base)) {
+		err = PTR_ERR(priv->ai_reg_base);
 		goto fail_dma_alloc;
 	}