mfd: cs5535-mfd: Use PLATFORM_DEVID_* defines and tidy error message

In most contexts '-1' doesn't really mean much to the casual observer.
In almost all cases, it's better to use a human readable define.  In
this case PLATFORM_DEVID_* defines have already been provided for this
purpose.

While we're here, let's be specific about the 'MFD devices' which
failed.  It will help when trying to distinguish which of the 2 sets
of sub-devices we actually failed to register.
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Reviewed-by: Daniel Thompson <daniel.thompson@linaro.org>

drivers/mfd/cs5535-mfd.c

@@ -127,10 +127,11 @@ static int cs5535_mfd_probe(struct pci_dev *pdev,
 		cs5535_mfd_cells[i].id = 0;
 	}
 
-	err = mfd_add_devices(&pdev->dev, -1, cs5535_mfd_cells,
+	err = mfd_add_devices(&pdev->dev, PLATFORM_DEVID_NONE, cs5535_mfd_cells,
 			      ARRAY_SIZE(cs5535_mfd_cells), NULL, 0, NULL);
 	if (err) {
-		dev_err(&pdev->dev, "MFD add devices failed: %d\n", err);
+		dev_err(&pdev->dev,
+			"Failed to add CS5535 sub-devices: %d\n", err);
 		goto err_disable;
 	}