net: hns3: add 5ms delay before clear firmware reset irq source

Currently the reset process in hns3 and firmware watchdog init process is
asynchronous. we think firmware watchdog initialization is completed
before hns3 clear the firmware interrupt source. However, firmware
initialization may not complete early.

so we add delay before hns3 clear firmware interrupt source and 5 ms delay
is enough to avoid second firmware reset interrupt.

Fixes: c1a81619 ("net: hns3: Add mailbox interrupt handling to PF driver")
Signed-off-by: Jie Wang <wangjie125@huawei.com>
Signed-off-by: Jijie Shao <shaojijie@huawei.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>