igc: Remove unused MII_CR_LOOPBACK

MII_CR_LOOPBACK masks not in use in i225 device and can be removed.
Signed-off-by: Sasha Neftin <sasha.neftin@intel.com>
Tested-by: Dvora Fuxbrumer <dvorax.fuxbrumer@linux.intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>

drivers/net/ethernet/intel/igc/igc_defines.h

@@ -441,7 +441,6 @@
 #define MII_CR_RESTART_AUTO_NEG	0x0200  /* Restart auto negotiation */
 #define MII_CR_POWER_DOWN	0x0800  /* Power down */
 #define MII_CR_AUTO_NEG_EN	0x1000  /* Auto Neg Enable */
-#define MII_CR_LOOPBACK		0x4000  /* 0 = normal, 1 = loopback */
 
 /* PHY Status Register */
 #define MII_SR_LINK_STATUS	0x0004 /* Link Status 1 = link */