staging: vt6656: Remove unnecesssary NULL check

pFifoHead points to tx_buffer->fifo_head which can never be NULL.
We also don't need to check for tx_buffer being NULL instead, since it
always points to ->Data of struct vnt_usb_send_context - the pointer to
which was checked before calling s_vGenerateTxParameter().

Silences a dereference before NULL check warning reported by the coverity
scanner in CID 1127221.

Cc: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Tobias Klauser <tklauser@distanz.ch>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/vt6656/rxtx.c

@@ -813,9 +813,6 @@ static u16 s_vGenerateTxParameter(struct vnt_private *pDevice,
 	else if (wFifoCtl & FIFOCTL_AUTO_FB_1)
 		byFBOption = AUTO_FB_1;
 
-	if (!pFifoHead)
-		return 0;
-
 	if (byPktType == PK_TYPE_11GB || byPktType == PK_TYPE_11GA) {
 		if (need_rts) {
 			struct vnt_rrv_time_rts *pBuf =