net: hns3: optimize code of hns3_parse_vlan_tag() function

driver inclusion
category: bugfix
bugzilla: NA
CVE: NA

This patch modifies the logic of two code in function hns3_parse_vlan_tag()
to reduce the indentation level. It does not affect the original function
of the code.

Signed-off-by: Guangbin Huang <huangguangbin2@huawei.com>
Reviewed-by: Yunsheng Lin <linyunsheng@huawei.com>
Reviewed-by: Zhong Zhaohui <zhongzhaohui@huawei.com>
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>