crypto: hisilicon/sec2 - Fix false-positive warning of uninitialised qp_ctx

Fix the false-positive warning of qp_ctx being unitialised in
sec_request_init.  The value of ctx_q_num defaults to 2 and is
guaranteed to be non-zero.

Thus qp_ctx is always initialised.  However, the compiler is
not aware of this constraint on ctx_q_num.  Restructure the loop
so that it is obvious to the compiler that ctx_q_num cannot be
zero.

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Reviewed-by: Longfang Liu <liulongfang@huawei.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>