coresight: ultrasoc-smb: fix return value check in smb_init_data_buffer()

platform_get_resource() returns NULL pointer not PTR_ERR(), replace
the IS_ERR() check with NULL pointer check.
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Link: https://lore.kernel.org/r/20230118074920.1772141-1-yangyingliang@huawei.com

drivers/hwtracing/coresight/ultrasoc-smb.c

@@ -455,7 +455,7 @@ static int smb_init_data_buffer(struct platform_device *pdev,
 	void *base;
 
 	res = platform_get_resource(pdev, IORESOURCE_MEM, SMB_BUF_ADDR_RES);
-	if (IS_ERR(res)) {
+	if (!res) {
 		dev_err(&pdev->dev, "SMB device failed to get resource\n");
 		return -EINVAL;
 	}