crypto: hisilicon/qm - clear used reference count when start qp

The used reference count is used for counting the number of 'sqe' which
is under processing. This reference count should be cleared as starting
'qp', otherwise the 'used' will be messy when allocating this 'qp' again.

Fixes: 5308f660("crypto: hisilicon - QM memory management...")
Signed-off-by: Shukun Tan <tanshukun1@huawei.com>
Signed-off-by: Yang Shen <shenyang39@huawei.com>
Reviewed-by: Zhou Wang <wangzhou1@hisilicon.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>