guest.h: Condition operator fix of foreach_vcpu loop
The for loop statement should work in both & and &&, but it seems
make more sense to have && when executing a condtion.
#define foreach_vcpu(idx, vm, vcpu) \
for (idx = 0, vcpu = vm->hw.vcpu_array[idx]; \
- (idx < vm->hw.num_vcpus) & (vcpu != NULL); \
+ (idx < vm->hw.num_vcpus) && (vcpu != NULL); \
idx++, vcpu = vm->hw.vcpu_array[idx])
