RDMA/irdma: Fix potential NULL-ptr-dereference

in_dev_get() can return NULL which will cause a failure once idev is
dereferenced in in_dev_for_each_ifa_rtnl(). This patch adds a
check for NULL value in idev beforehand.

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

Fixes: 146b975 ("RDMA/irdma: Add connection manager")
Signed-off-by: Nikita Zhandarovich <n.zhandarovich@fintech.ru>
Link: https://lore.kernel.org/r/20230126185230.62464-1-n.zhandarovich@fintech.ru
Reviewed-by: Sindhu Devale <sindhu.devale@intel.com>
Signed-off-by: Leon Romanovsky <leon@kernel.org>

Author: Nikita Zhandarovich

drivers/infiniband/hw/irdma/cm.c

@@ -1722,6 +1722,9 @@ static int irdma_add_mqh_4(struct irdma_device *iwdev,
 			continue;
 
 		idev = in_dev_get(ip_dev);
+		if (!idev)
+			continue;
+
 		in_dev_for_each_ifa_rtnl(ifa, idev) {
 			ibdev_dbg(&iwdev->ibdev,
 				  "CM: Allocating child CM Listener forIP=%pI4, vlan_id=%d, MAC=%pM\n",