kvm_write_tsc() converts from guest TSC to microseconds, not nanoseconds
as intended. The result is that the window for matching is 1000 seconds,
not 1 second.

Microsecond precision is enough for checking whether the TSC write delta
is within the heuristic values, so use it instead of nanoseconds.

Noted by Avi Kivity.
Signed-off-by: NMarcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: NAvi Kivity <avi@redhat.com>