RDMA/irdma: Fix potential NULL-ptr-dereference

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: 146b9756f14c ("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>