sched: core: Use hrtimer_start[_expires]()

hrtimer_start() now enforces a timer interrupt when an already expired
timer is enqueued.

Get rid of the __hrtimer_start_range_ns() invocations and the loops
around it.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Peter Zijlstra <peterz@infradead.org>
Cc: Preeti U Murthy <preeti@linux.vnet.ibm.com>
Cc: Viresh Kumar <viresh.kumar@linaro.org>
Cc: Marcelo Tosatti <mtosatti@redhat.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Link: http://lkml.kernel.org/r/20150414203502.531131739@linutronix.de


Signed-off-by: Thomas Gleixner <tglx@linutronix.de>