crypto: caam/qi - simplify error path for context allocation

Wang Qing reports that IS_ERR_OR_NULL() should be matched with
PTR_ERR_OR_ZERO(), not PTR_ERR().

As it turns out, the error path always returns an error code,
i.e. NULL is never returned.
Update the code accordingly - s/IS_ERR_OR_NULL/IS_ERR.

Reported-by: Wang Qing <wangqing@vivo.com>
Signed-off-by: Horia Geantă <horia.geanta@nxp.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>