UBUNTU: SAUCE: opennsl: bcm-knet: check for null sinfo to avoid a null pointer dereference

BugLink: https://launchpad.net/bugs/1718388

sinfo can potentially be null, so add a null check to avoid a null
pointer deference on sinfo->info_id.

Detected by CoverityScan CID#1456902 ("Dereference before null check")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Acked-by: Juerg Haefliger <juerg.haefliger@canonical.com>
Acked-by: Stefan Bader <stefan.bader@canonical.com>
[kleber: adapted for new version path]
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>

ubuntu/opennsl/OpenNSL/sdk-6.5.10-gpl-modules/systems/linux/kernel/modules/bcm-knet/bcm-knet.c

@@ -6357,7 +6357,8 @@ bkn_get_next_dma_event(kcom_msg_dma_info_t *kmsg)
             sinfo = bkn_sinfo_from_unit(dev_no);
         }
 
-        if ((sinfo->inst_id != 0) && ((sinfo->inst_id & (1 << dev_evt)) == 0)){
+        if (sinfo && (sinfo->inst_id != 0) &&
+	    ((sinfo->inst_id & (1 << dev_evt)) == 0)) {
             DBG_INST((" %s skip dev(%d)\n",__FUNCTION__,dev_evt));
             continue;
         }