kvm: x86: memset whole irq_eoi

gcc 7 warns:
arch/x86/kvm/ioapic.c: In function 'kvm_ioapic_reset':
arch/x86/kvm/ioapic.c:597:2: warning: 'memset' used with length equal to number of elements without multiplication by element size [-Wmemset-elt-size]

And it is right. Memset whole array using sizeof operator.

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Radim Krčmář <rkrcmar@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: x86@kernel.org
Cc: kvm@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Cc: stable@vger.kernel.org
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
[Added x86 subject tag]
Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>