timer: Initialize the field slack of timer_list

TIMER_INITIALIZER() should initialize the field slack of timer_list as
__init_timer() does.

Signed-off-by: Changli Gao <xiaosuo@gmail.com>
Cc: Arjan van de Ven <arjan@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

include/linux/timer.h

@@ -54,6 +54,7 @@ extern struct tvec_base boot_tvec_bases;
 		.expires = (_expires),				\
 		.data = (_data),				\
 		.base = &boot_tvec_bases,			\
+		.slack = -1,					\
 		__TIMER_LOCKDEP_MAP_INITIALIZER(		\
 			__FILE__ ":" __stringify(__LINE__))	\
 	}