usb: gadget: f_ncm: remove spurious if statement

the current logic is:

  struct sk_buff  *skb2 = NULL;
  ...

  if (!skb && !ncm->skb_tx_data)
    return NULL;

  if (skb) {
    ...
  } else if (ncm->skb_tx_data)
    ...
  }

  return skb2;

Which means that first if statement is simply not needed.

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/20210701114834.884597-4-zenczykowski@gmail.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/gadget/function/f_ncm.c

@@ -1025,9 +1025,6 @@ static struct sk_buff *ncm_wrap_ntb(struct gether *port,
 	const int rem = le16_to_cpu(ntb_parameters.wNdpInPayloadRemainder);
 	const int dgram_idx_len = 2 * 2 * opts->dgram_item_len;
 
-	if (!skb && !ncm->skb_tx_data)
-		return NULL;
-
 	if (skb) {
 		/* Add the CRC if required up front */
 		if (ncm->is_crc) {