net: hns3: add checking for vf id of mailbox

Add checking for vf id of mailbox, in order to avoid array
out-of-bounds risk.

Signed-off-by: Jian Shen <shenjian15@huawei.com>
Signed-off-by: Jijie Shao <shaojijie@huawei.com>
Reviewed-by: Sunil Goutham <sgoutham@marvell.com>
Signed-off-by: David S. Miller <davem@davemloft.net>