Fix null pointer dereference reported in coverity scan. Coverity issue: 378882 Fixes: 5d75517beffe ("vdpa/ifc/base: access block device registers") Signed-off-by: Andy Pei <andy.pei@intel.com> Acked-by: Xiao Wang <xiao.w.wang@intel.com> Reviewed-by: Maxime Coquelin <maxime.coquelin@redhat.com>