watchdog: rti: Fix off-by-one in heartbeat recovery

According to AM62x TRM WDT period is (RTIDWDPRLD + 1) * (2^13) / RTICLK1,
Fix the heartbeat recovery. In practice this doesn't affect rounded
heatbeat in seconds, but it does correct 4% of error in milliseconds,
for, say, default 60s heartbeat. This affects last_ping calculation.

Signed-off-by: Alexander Sverdlin <alexander.sverdlin@siemens.com>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Link: https://lore.kernel.org/r/20241126073646.126752-1-alexander.sverdlin@siemens.com
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@linux-watchdog.org>

Author: ccpalex

drivers/watchdog/rti_wdt.c

@@ -273,7 +273,8 @@ static int rti_wdt_probe(struct platform_device *pdev)
 
 		set_bit(WDOG_HW_RUNNING, &wdd->status);
 		time_left_ms = rti_wdt_get_timeleft_ms(wdd);
-		heartbeat_ms = readl(wdt->base + RTIDWDPRLD);
+		/* AM62x TRM: texp = (RTIDWDPRLD + 1) * (2^13) / RTICLK1 */
+		heartbeat_ms = readl(wdt->base + RTIDWDPRLD) + 1;
 		heartbeat_ms <<= WDT_PRELOAD_SHIFT;
 		heartbeat_ms *= 1000;
 		do_div(heartbeat_ms, wdt->freq);