Otherwise its possible for an unrelated KVM_REQ_UPDATE_CLOCK (such as due to CPU
migration) to clear the bit.

Noticed by Paolo Bonzini.
Reviewed-by: NGleb Natapov <gleb@redhat.com>
Reviewed-by: NGlauber Costa <glommer@parallels.com>
Signed-off-by: NMarcelo Tosatti <mtosatti@redhat.com>