staging: dgrp: fix potential NULL defereference issue

Fix a coccinelle warning catched by Fengguang's 0-DAY system:
+ drivers/staging/dgrp/dgrp_net_ops.c:1061:11-27: ERROR: nd is NULL but dereferenced.

Put the "done:" label a bit down would solve this issue.

Cc: Fengguang Wu <fengguang.wu@intel.com>
Cc: Julia Lawall <julia.lawall@lip6.fr>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Yuanhan Liu <yuanhan.liu@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>