igb: remove never changed variable `ret_val'

The variable used for return status in `igb_write_xmdio_reg' function
is never changed  and this function is just need return 0. Thus, the
`ret_val' can be removed and return 0 at the end of the
`igb_write_xmdio_reg' function.
Signed-off-by: Jason Wang <wangborong@cdjrlc.com>
Tested-by: Gurucharan G <gurucharanx.g@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>

drivers/net/ethernet/intel/igb/e1000_i210.c

@@ -792,7 +792,6 @@ s32 igb_write_xmdio_reg(struct e1000_hw *hw, u16 addr, u8 dev_addr, u16 data)
  **/
 s32 igb_init_nvm_params_i210(struct e1000_hw *hw)
 {
-	s32 ret_val = 0;
 	struct e1000_nvm_info *nvm = &hw->nvm;
 
 	nvm->ops.acquire = igb_acquire_nvm_i210;
@@ -813,7 +812,7 @@ s32 igb_init_nvm_params_i210(struct e1000_hw *hw)
 		nvm->ops.validate = NULL;
 		nvm->ops.update   = NULL;
 	}
-	return ret_val;
+	return 0;
 }
 
 /**