igc: Remove duplicated IGC_RXPBS macro

This patch remove the IGC_RXPBS macro defined in line 233 since it is
already defined in line 18 with the exactly same value.

Signed-off-by: Andre Guedes <andre.guedes@intel.com>
Tested-by: Aaron Brown <aaron.f.brown@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>