acpi-power-meter: Don't leak ACPI error codes to userspace

If the ACPI methods return an error code, we must return -EINVAL to userspace
to flag the error.  Right now we pass the (positive) number right through,
which causes echo to keep writing bogus values.
Signed-off-by: Darrick J. Wong <djwong@us.ibm.com>
Acked-by: Jean Delvare <khali@linux-fr.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Len Brown <len.brown@intel.com>

drivers/acpi/power_meter.c

@@ -294,7 +294,11 @@ static int set_acpi_trip(struct acpi_power_meter_resource *resource)
 		return -EINVAL;
 	}
 
-	return data;
+	/* _PTP returns 0 on success, nonzero otherwise */
+	if (data)
+		return -EINVAL;
+
+	return 0;
 }
 
 static ssize_t set_trip(struct device *dev, struct device_attribute *devattr,