valgrind/i386: avoid false positives on KVM_SET_VCPU_EVENTS ioctl

struct kvm_vcpu_events contains reserved fields. Let's use a
designated initializer to avoid false positives in valgrind.

Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
