drivers/net/sfc: fix sparse warning: symbol shadows an earlier one

Impact: Move variable declaration as close to their usage as possible.

Fix this sparse warning:
  drivers/net/sfc/tenxpress.c:589:22: warning: symbol 'link_ok' shadows an earlier one
  drivers/net/sfc/tenxpress.c:575:30: originally declared here

Signed-off-by: Hannes Eder <hannes@hanneseder.net>
Acked-by: Ben Hutchings <bhutchings@solarflare.com>
Signed-off-by: David S. Miller <davem@davemloft.net>