hash: fix ring size

hash: fix ring size

Ring stores the free slots available to be used in the key table.
The ring size was being increased by 1, because of the dummy slot,
used for key misses, but this is not actually stored in the ring,
so there is no need to increase it.

Fixes: 5915699153d7 ("hash: fix scaling by reducing contention")

Signed-off-by: Pablo de Lara <pablo.de.lara.guarch@intel.com>
Acked-by: Saikrishna Edupuganti <saikrishna.edupuganti@intel.com>