mfd: Improve diagnostics for WM8350 ID register probe

Check the return value of the device I/O functions when reading the
ID registers so we can provide a more useful diagnostic when we're
having trouble talking to the device.

Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Samuel Ortiz <sameo@openedhand.com>

drivers/mfd/wm8350-core.c

@@ -1297,14 +1297,29 @@ static void wm8350_client_dev_register(struct wm8350 *wm8350,
 int wm8350_device_init(struct wm8350 *wm8350, int irq,
 		       struct wm8350_platform_data *pdata)
 {
-	int ret = -EINVAL;
+	int ret;
 	u16 id1, id2, mask_rev;
 	u16 cust_id, mode, chip_rev;
 
 	/* get WM8350 revision and config mode */
-	wm8350->read_dev(wm8350, WM8350_RESET_ID, sizeof(id1), &id1);
-	wm8350->read_dev(wm8350, WM8350_ID, sizeof(id2), &id2);
-	wm8350->read_dev(wm8350, WM8350_REVISION, sizeof(mask_rev), &mask_rev);
+	ret = wm8350->read_dev(wm8350, WM8350_RESET_ID, sizeof(id1), &id1);
+	if (ret != 0) {
+		dev_err(wm8350->dev, "Failed to read ID: %d\n", ret);
+		goto err;
+	}
+
+	ret = wm8350->read_dev(wm8350, WM8350_ID, sizeof(id2), &id2);
+	if (ret != 0) {
+		dev_err(wm8350->dev, "Failed to read ID: %d\n", ret);
+		goto err;
+	}
+
+	ret = wm8350->read_dev(wm8350, WM8350_REVISION, sizeof(mask_rev),
+			       &mask_rev);
+	if (ret != 0) {
+		dev_err(wm8350->dev, "Failed to read revision: %d\n", ret);
+		goto err;
+	}
 
 	id1 = be16_to_cpu(id1);
 	id2 = be16_to_cpu(id2);