crypto: nitrox - avoid double free on error path in nitrox_sriov_init()

If alloc_workqueue() fails in nitrox_mbox_init() it deallocates
ndev->iov.vfdev and returns error code, but then nitrox_sriov_init()
calls nitrox_sriov_cleanup() where ndev->iov.vfdev is deallocated
again.

Fix this by nulling ndev->iov.vfdev after the first deallocation.

Found by Linux Verification Center (linuxtesting.org) with SVACE.

Fixes: 9e5de3e0 ("crypto: cavium/nitrox - Add mailbox...")
Signed-off-by: Natalia Petrova <n.petrova@fintech.ru>
Signed-off-by: Alexey Khoroshilov <khoroshilov@ispras.ru>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

drivers/crypto/cavium/nitrox/nitrox_mbx.c

@@ -195,6 +195,7 @@ int nitrox_mbox_init(struct nitrox_device *ndev)
 	ndev->iov.pf2vf_wq = alloc_workqueue("nitrox_pf2vf", 0, 0);
 	if (!ndev->iov.pf2vf_wq) {
 		kfree(ndev->iov.vfdev);
+		ndev->iov.vfdev = NULL;
 		return -ENOMEM;
 	}
 	/* enable pf2vf mailbox interrupts */