sched: avoid ksoftirqd wakeups when starting the hrtick timer

Calling hrtimer_start() to start the hrtick timer is not safe, as it
may wake up ksoftirqd.  Use __hrtimer_start_range_ns() instead.

Signed-off-by: Fabio Checconi <f.checconi@gmail.com>
Signed-off-by: Juri Lelli <juri.lelli@gmail.com>