refine definition for foreach_vcpu

foreach_vcpu will go through all vcpu_array and only call the following
code when vcpu != NULL

Signed-off-by: Jason Chen CJ <jason.cj.chen@intel.com>
Reviewed-by: Zhao Yakui <yakui.zhao@intel.com>
Acked-by: Eddie Dong <eddie.dong@intel.com>

Author: JasonChenCJ

hypervisor/include/arch/x86/guest/guest.h

@@ -20,9 +20,9 @@
 
 #define foreach_vcpu(idx, vm, vcpu)				\
 	for (idx = 0U, vcpu = vm->hw.vcpu_array[idx];		\
-		(idx < vm->hw.num_vcpus) && (vcpu != NULL);	\
-		idx++, vcpu = vm->hw.vcpu_array[idx])
-
+		idx < vm->hw.num_vcpus;				\
+		idx++, vcpu = vm->hw.vcpu_array[idx])		\
+		if (vcpu)
 
 /* the index is matched with emulated msrs array*/
 #define IDX_TSC_DEADLINE		0U