crypto/octeontx: fix null pointer dereferencing

crypto/octeontx: fix null pointer dereferencing

The function otx_cpt_get_resource() would be setting the pointer
'instance'. In case of error, 'instance' would be set to NULL, and
returns rte_errno. If rte_errno when 'instance' is set to NULL, it can
lead to NULL pointer dereferencing.

Coverity Issue: 323486, 323489
Fixes: bfe2ae495ee2 ("crypto/octeontx: add PMD skeleton")
Fixes: 0961348fdf52 ("crypto/octeontx: add queue pair functions")

Signed-off-by: Anoob Joseph <anoob.joseph@caviumnetworks.com>