Fix overflow calculation for reload_value.

Please,  note that this patch fixes upstream bug. See:

https://devzone.nordicsemi.com/f/nordic-q-a/51674/maximum-reload-time-for-wdt

Author: manchoz

targets/TARGET_NORDIC/TARGET_NRF5x/TARGET_NRF52/watchdog_api.c

@@ -69,7 +69,7 @@ watchdog_status_t hal_watchdog_stop(void)
 uint32_t hal_watchdog_get_reload_value(void)
 {
     // Convert to milliseconds from 32768 Hz clock ticks.
-    return nrf_wdt_reload_value_get() / 32768U * 1000;
+    return (uint64_t)nrf_wdt_reload_value_get() / 32768U * 1000;
 }
 
 watchdog_features_t hal_watchdog_get_platform_features(void)

targets/TARGET_NORDIC/TARGET_NRF5x/TARGET_SDK_15_0/modules/nrfx/drivers/src/nrfx_wdt.c

@@ -90,7 +90,7 @@ nrfx_err_t nrfx_wdt_init(nrfx_wdt_config_t const * p_config,
 
     nrf_wdt_behaviour_set(p_config->behaviour);
 
-    nrf_wdt_reload_value_set((p_config->reload_value * 32768) / 1000);
+    nrf_wdt_reload_value_set(((uint64_t)p_config->reload_value * 32768) / 1000);
 
     NRFX_IRQ_PRIORITY_SET(WDT_IRQn, p_config->interrupt_priority);
     NRFX_IRQ_ENABLE(WDT_IRQn);