timekeeping: Use proper seqcount initializer

tk_core.seq is initialized open coded, but that misses to initialize the
lockdep map when lockdep is enabled. Lockdep splats involving tk_core seq
consequently lack a name and are hard to read.

Use the proper initializer which takes care of the lockdep map
initialization.

[ tglx: Massaged changelog ]
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: peterz@infradead.org
Cc: tj@kernel.org
Cc: johannes.berg@intel.com
Link: https://lkml.kernel.org/r/20181128234325.110011-12-bvanassche@acm.org

kernel/time/timekeeping.c

@@ -45,7 +45,9 @@ enum timekeeping_adv_mode {
 static struct {
 	seqcount_t		seq;
 	struct timekeeper	timekeeper;
-} tk_core ____cacheline_aligned;
+} tk_core ____cacheline_aligned = {
+	.seq = SEQCNT_ZERO(tk_core.seq),
+};
 
 static DEFINE_RAW_SPINLOCK(timekeeper_lock);
 static struct timekeeper shadow_timekeeper;