sched: task: Fix to initialize the task-specific data

Summary:
- I noticed that getopt() test in ostest wailed with
  esp32-devkitc:smp and spresense:smp
- Finally, I found that the task-specific data is not
  initialized.
- This commit fixes this issue

Impact:
- None

Testing:
- Tested with ostest esp32-devkitc:smp and spresense:smp

Signed-off-by: Masayuki Ishikawa <Masayuki.Ishikawa@jp.sony.com>

sched/task/task_init.c

@@ -137,6 +137,10 @@ int nxtask_init(FAR struct task_tcb_s *tcb, const char *name, int priority,
   group->tg_libvars = up_stack_frame(&tcb->cmn, sizeof(struct libvars_s));
   DEBUGASSERT(group->tg_libvars != NULL);
 
+  /* Initialize the task-specific data */
+
+  memset(group->tg_libvars, 0, sizeof(struct libvars_s));
+
   /* Save the allocated task data in TLS */
 
   tls_set_taskdata(&tcb->cmn);