Reduce increase progression of aspiration window

Currently, in case of fail high/low we research with
a window increased by 2*AspirationDelta at first
attempt, this patch instead makes the research be
done with an increase of just AspirationDelta size,
in case of a consecutive fail we will widen to
2*AspirationDelta and so on.

After Joona's test:
Orig - Mod: 850 - 890

Signed-off-by: Marco Costalba <mcostalba@gmail.com>