e1000: fix kernel-doc argument being missing

Due to historical reason, 'phy_data' has never been included in the
kernel doc. Fix it so that the requirement could be fulfilled.

Signed-off-by: Jean Sacren <sakiwit@gmail.com>
Tested-by: Aaron Brown <aaron.f.brown@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>