net: ethtool: Fix the panic caused by dev being null when dumping coalesce

net: ethtool: Fix the panic caused by dev being null when dumping coalesce

syzbot reported a general protection fault caused by a null pointer
dereference in coalesce_fill_reply(). The issue occurs when req_base->dev
is null, leading to an invalid memory access.

This panic occurs if dumping coalesce when no device name is specified.

Fixes: f750dfe825b9 ("ethtool: provide customized dim profile management")
Reported-by: syzbot+e77327e34cdc8c36b7d3@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=e77327e34cdc8c36b7d3
Signed-off-by: Heng Qi <hengqi@linux.alibaba.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>