cpumask: use zalloc_cpumask_var() where possible

Remove open-coded zalloc_cpumask_var() and zalloc_cpumask_var_node().

Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 897bff3..034a798 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -738,8 +738,7 @@
 	bool called = true;
 	struct kvm_vcpu *vcpu;
 
-	if (alloc_cpumask_var(&cpus, GFP_ATOMIC))
-		cpumask_clear(cpus);
+	zalloc_cpumask_var(&cpus, GFP_ATOMIC);
 
 	spin_lock(&kvm->requests_lock);
 	me = smp_processor_id();