drivers/net/cxgb3: comment out dead code

The function 'vsc8211_set_speed_duplex' is not used, so comment it
out.  For 'vsc8211_set_automdi' the function 'vsc8211_set_speed_duplex'
is the only caller, so comment it out as well.

Fix this (sparse) warning:

  drivers/net/cxgb3/vsc8211.c:269: warning: 'vsc8211_set_automdi' defined but not used
  drivers/net/cxgb3/vsc8211.c:295:5: warning: symbol 'vsc8211_set_speed_duplex' was not declared. Should it be static?

Signed-off-by: Hannes Eder <hannes@hanneseder.net>
Signed-off-by: David S. Miller <davem@davemloft.net>