watchdog: shwdt: fix usage of mod_timer

Fix the usage of mod_timer() and make the driver usable. mod_timer() must
be called with an absolute timeout in jiffies. The old implementation
used a relative timeout thus the hardware watchdog was never triggered.

Signed-off-by: David Engraf <david.engraf@sysgo.com>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>
Signed-off-by: Wim Van sebroeck <wim@iguana.be>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Cc: stable <stable@kernel.org>

drivers/watchdog/shwdt.c

@@ -64,7 +64,7 @@
  * misses its deadline, the kernel timer will allow the WDT to overflow.
  */
 static int clock_division_ratio = WTCSR_CKS_4096;
-#define next_ping_period(cks)	msecs_to_jiffies(cks - 4)
+#define next_ping_period(cks)	(jiffies + msecs_to_jiffies(cks - 4))
 
 static const struct watchdog_info sh_wdt_info;
 static struct platform_device *sh_wdt_dev;