watchdog: Fix typo in comment

Signed-off-by: Arash Fotouhi <arash@arashfotouhi.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: loberman@redhat.com
Cc: vincent.whitchurch@axis.com
Link: http://lkml.kernel.org/r/1553308112-3513-1-git-send-email-arash@arashfotouhi.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>