ixgbe: Eliminate useless message and improve logic

Remove a useless log message and improve the logic for setting
a PHY address from the contents of the MNG_IF_SEL register.

Signed-off-by: Mark Rustad <mark.d.rustad@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>