watchdog: orion: use 0 for unset heartbeat

If the heartbeat module param is not specified we would get an error
message

  watchdog: f1020300.watchdog: driver supplied timeout (4294967295) out of range
  watchdog: f1020300.watchdog: falling back to default timeout (171)

This is because we were initialising heartbeat to -1. By removing the
initialisation (thus letting the C run time initialise it to 0) we
silence the warning message and the default timeout is still used.
Signed-off-by: Chris Packham <chris.packham@alliedtelesis.co.nz>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Link: https://lore.kernel.org/r/20200313031312.1485-1-chris.packham@alliedtelesis.co.nzSigned-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@linux-watchdog.org>

drivers/watchdog/orion_wdt.c

@@ -52,7 +52,7 @@
 #define WDT_A370_RATIO		(1 << WDT_A370_RATIO_SHIFT)
 
 static bool nowayout = WATCHDOG_NOWAYOUT;
-static int heartbeat = -1;		/* module parameter (seconds) */
+static int heartbeat;		/* module parameter (seconds) */
 
 struct orion_watchdog;