cryptodev: fix asymmetric private session variable size

cryptodev: fix asymmetric private session variable size

When creating the asymmetric session mempool, the maximum private
session size of all devices is used when creating the mempool
object size.
The return value for ``rte_cryptodev_asym_get_private_session_size``
is unsigned int, whereas the variable was uint8_t, leading to a
possible overflow issue.

To fix this, the variable for private session size is now changed to
unsigned int to match the function return type.

Fixes: 1f1e4b7cbaad ("cryptodev: use single mempool for asymmetric session")
Reported-by: Arek Kusztal <arkadiuszx.kusztal@intel.com>
Signed-off-by: Ciara Power <ciara.power@intel.com>
Acked-by: Fan Zhang <roy.fan.zhang@intel.com>
Acked-by: Arek Kusztal <arkadiuszx.kusztal@intel.com>