sound: Use hrtimer_resolution instead of hrtimer_get_res()

No point in converting a timespec now that the value is directly
accessible. Get rid of the null check while at it. Resolution is
guaranteed to be > 0.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Takashi Iwai <tiwai@suse.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>
Cc: Jaroslav Kysela <perex@perex.cz>
Cc: alsa-devel@alsa-project.org
Link: http://lkml.kernel.org/r/20150414203500.799133359@linutronix.de


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