igb: Fix memory leak in igb_get_module_eeprom()

Fix a memory leak in the igb_get_module_eeprom() error handling path.
Detected by Coverity: CID 1016508.

Signed-off-by: Christian Engelmayer <cengelma@gmx.at>
Tested-by: Jeff Pieper <jeffrey.e.pieper@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>