watchdog: mlx-wdt: Parameter desctiption warning fix

Add parameter desription to fix warning.

Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202310241044.lvqeOGli-lkp@intel.com
Signed-off-by: Michael Shych <michaelsh@nvidia.com>
Signed-off-by: Vadim Pasternak <vadimp@nvidia.com>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Link: https://lore.kernel.org/r/20231026082558.12142-1-michaelsh@nvidia.com
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@linux-watchdog.org>

Author: mshych

drivers/watchdog/mlx_wdt.c

@@ -39,6 +39,7 @@
  * @tleft_idx:	index for direct access to time left register;
  * @ping_idx:	index for direct access to ping register;
  * @reset_idx:	index for direct access to reset cause register;
+ * @regmap_val_sz: size of value in register map;
  * @wd_type:	watchdog HW type;
  */
 struct mlxreg_wdt {