drm/i915/pmu: replace cpumask_weight with cpumask_empty where appropriate

i915_pmu_cpu_online() calls cpumask_weight() to check if any bit of a
given cpumask is set. We can do it more efficiently with cpumask_empty()
because cpumask_empty() stops traversing the cpumask as soon as it finds
first set bit, while cpumask_weight() counts all bits unconditionally.

Signed-off-by: Yury Norov <[e-mail]>
Reviewed-by: Tvrtko Ursulin <[e-mail]>

drivers/gpu/drm/i915/i915_pmu.c

···
 	GEM_BUG_ON(!pmu->base.event_init);
 
 	/* Select the first online CPU as a designated reader. */
-	if (!cpumask_weight(&i915_pmu_cpumask))
+	if (cpumask_empty(&i915_pmu_cpumask))
 		cpumask_set_cpu(cpu, &i915_pmu_cpumask);
 
 	return 0;