ixgbe: add error checks when initializing the PHY

Ignoring errors when attempting to identify the PHY can lead to a crash.
Specifically in the case of FW controlled PHYs where the PHY read/write
operations are set to NULL.

Removed redundant comment.

Signed-off-by: Emil Tantilov <emil.s.tantilov@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>