usb: gadget: f_ncm: remove check for NULL skb_tx_data in timer function

This condition is already checked for in ncm_wrap_ntb(),
except that that check is done with eth_dev->lock held
(it is grabbed by eth_start_xmit).

It's best to not be reaching into ncm struct without locks held.

Cc: Brooke Basile <brookebasile@gmail.com>
Cc: "Bryan O'Donoghue" <bryan.odonoghue@linaro.org>
Cc: Felipe Balbi <balbi@kernel.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Lorenzo Colitti <lorenzo@google.com>
Signed-off-by: Maciej Żenczykowski <maze@google.com>
Link: https://lore.kernel.org/r/20210701114834.884597-3-zenczykowski@gmail.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/gadget/function/f_ncm.c

@@ -1156,8 +1156,7 @@ static enum hrtimer_restart ncm_tx_timeout(struct hrtimer *data)
 	struct f_ncm *ncm = container_of(data, struct f_ncm, task_timer);
 	struct net_device *netdev = READ_ONCE(ncm->netdev);
 
-	/* Only send if data is available. */
-	if (netdev && ncm->skb_tx_data) {
+	if (netdev) {
 		/* XXX This allowance of a NULL skb argument to ndo_start_xmit
 		 * XXX is not sane.  The gadget layer should be redesigned so
 		 * XXX that the dev->wrap() invocations to build SKBs is transparent