ethtool: always write dev in ethnl_parse_header_dev_get

ethtool: always write dev in ethnl_parse_header_dev_get

Commit d9f75300d857 ("ethtool: fix null-ptr-deref on ref tracker")
made the write to req_info.dev conditional, but as Eric points out
in a different follow up the structure is often allocated on the
stack and not kzalloc()'d so seems safer to always write the dev,
in case it's garbage on input.

Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>