sched/rq_clock: Consolidate the ordering of the rq_clock methods

update_rq_clock_task() and update_rq_clock() we unnecessarily
spread across core.c, requiring an extra prototype line.

Move them next to each other and in the proper order.

Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>