scsi: snic: Return error code on memory allocation failure

If a call to mempool_create_slab_pool() in snic_probe() returns NULL,
return -ENOMEM to indicate failure. mempool_creat_slab_pool() only fails
if it cannot allocate memory.

https://bugzilla.kernel.org/show_bug.cgi?id=189061

Reported-by:  <bianpan2010@ruc.edu.cn>
Signed-off-by: Burak Ok <burak-kernel@bur0k.de>
Signed-off-by: Andreas Schaertl <andreas.schaertl@fau.de>
Acked-by: Narsimhulu Musini <nmusini@cisco.com>
Reviewed-by: Ewan D. Milne <emilne@redhat.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>