KVM: i8254: remove pit and kvm from kvm_kpit_state

kvm isn't ever used and pit can be accessed with container_of.
If you *really* need kvm, pit_state_to_pit(ps)->kvm.

Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>