scsi: libcxgbi: fix NULL pointer dereference in cxgbi_device_destroy()

If cxgb4i_ddp_init() fails then cdev->cdev2ppm will be NULL, so add a check
for NULL pointer before dereferencing it.

Link: https://lore.kernel.org/r/1576676731-3068-1-git-send-email-varun@chelsio.comSigned-off-by: Varun Prakash <varun@chelsio.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/scsi/cxgbi/libcxgbi.c

@@ -121,6 +121,7 @@ static inline void cxgbi_device_destroy(struct cxgbi_device *cdev)
 		"cdev 0x%p, p# %u.\n", cdev, cdev->nports);
 	cxgbi_hbas_remove(cdev);
 	cxgbi_device_portmap_cleanup(cdev);
+	if (cdev->cdev2ppm)
 		cxgbi_ppm_release(cdev->cdev2ppm(cdev));
 	if (cdev->pmap.max_connect)
 		cxgbi_free_big_mem(cdev->pmap.port_csk);