igc: Remove stale comment about Tx timestamping

The initial igc Tx timestamping implementation used only one register for
retrieving Tx timestamps. Commit 3ed247e ("igc: Add support for
multiple in-flight TX timestamps") added support for utilizing all four of
them e.g., for multiple domain support. Remove the stale comment/FIXME.

Fixes: 3ed247e ("igc: Add support for multiple in-flight TX timestamps")
Signed-off-by: Kurt Kanzenbach <kurt@linutronix.de>
Acked-by: Vinicius Costa Gomes <vinicius.gomes@intel.com>
Reviewed-by: Przemek Kitszel <przemyslaw.kitszel@intel.com>
Tested-by: Naama Meir <naamax.meir@linux.intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>

drivers/net/ethernet/intel/igc/igc_main.c

@@ -1642,10 +1642,6 @@ static netdev_tx_t igc_xmit_frame_ring(struct sk_buff *skb,
 
 	if (unlikely(test_bit(IGC_RING_FLAG_TX_HWTSTAMP, &tx_ring->flags) &&
 		     skb_shinfo(skb)->tx_flags & SKBTX_HW_TSTAMP)) {
-		/* FIXME: add support for retrieving timestamps from
-		 * the other timer registers before skipping the
-		 * timestamping request.
-		 */
 		unsigned long flags;
 		u32 tstamp_flags;