ixgbevf: Fix link speed message to support 100Mbps

The X540 can link at 100Mbps - fix the link speed indicator message to
show that value.

Signed-off-by: Greg Rose <gregory.v.rose@intel.com>
Tested-by: Sibai Li <sibai.li@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>