tg3: prevent use of uninitialized remote_adv and local_adv variables

tg3: prevent use of uninitialized remote_adv and local_adv variables

Some execution paths that jump to the fiber_setup_done label
could leave the remote_adv and local_adv variables uninitialized
and then use it.

Initialize this variables at the point of definition to avoid this.

Fixes: 85730a631f0c ("tg3: Add SGMII phy support for 5719/5718 serdes")
Co-developed-by: Alexandr Sapozhnikov <alsp705@gmail.com>
Signed-off-by: Alexandr Sapozhnikov <alsp705@gmail.com>
Signed-off-by: Alexey Simakov <bigalex934@gmail.com>
Reviewed-by: Pavan Chebbi <pavan.chebbi@broadcom.com>
Link: https://patch.msgid.link/20251014164736.5890-1-bigalex934@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>