ACPI: APD: Add kerneldoc for properties in struct apd_device_desc

commit 7ff55d174c ("ACPI / APD: Provide build-in properties of the
UART") added the struct property_entry *properties field to struct
apd_device_desc, but didn't add the kernel doc for it, so add it now.

Signed-off-by: Hanjun Guo <guohanjun@huawei.com>
[ rjw: Subject and changelog edits ]
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/acpi/acpi_apd.c

@@ -34,6 +34,7 @@ struct apd_private_data;
  * @flags: device flags like %ACPI_APD_SYSFS, %ACPI_APD_PM
  * @fixed_clk_rate: fixed rate input clock source for acpi device;
  *			0 means no fixed rate input clock source
+ * @properties: build-in properties of the device such as UART
  * @setup: a hook routine to set device resource during create platform device
  *
  * Device description defined as acpi_device_id.driver_data