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sched_clock_running is enabled early at bootup stage and never
disabled. So hint that to the compiler by using static_branch_likely()
rather than static_branch_unlikely().

The branch probability mis-annotation was introduced in the original
commit that converted the plain sched_clock_running flag to a static key:

  46457ea4 ("sched/clock: Use static key for sched_clock_running")

Steve further notes:

  | Looks like the confusion was the moving of the "!":
  |
  | -       if (unlikely(!sched_clock_running))
  | +       if (!static_branch_unlikely(&sched_clock_running))
  |
  | Where, it was unlikely that !sched_clock_running would be true, but
  | because the "!" was moved outside the "unlikely()" it makes the test
  | "likely()". That is, if we added an intermediate step, it would have
  | been:
  |
  |         if (!likely(sched_clock_running))
  |
  | which would have prevented the mistake that this patch fixes.

  [ mingo: Edited th...