wdt: Update uclass to make clear that the timeout is in ms

Convert name to show explicitly that we are using milliseconds. For a
watchdog timer this is precise enough.

No functional change intended.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>