staging: rtl8192u: Fix shadowed variable name

Fixes the following sparse warning:

drivers/staging/rtl8192u/ieee80211/ieee80211_tx.c:798:32: warning: symbol 'tcb_desc' shadows an earlier one
drivers/staging/rtl8192u/ieee80211/ieee80211_tx.c:550:24: originally declared here
Signed-off-by: Thomas Bracht Laumann Jespersen <t@laumann.xyz>
Link: https://lore.kernel.org/r/20210527192149.29686-1-t@laumann.xyzSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/rtl8192u/ieee80211/ieee80211_tx.c

@@ -795,7 +795,7 @@ int ieee80211_xmit(struct sk_buff *skb, struct net_device *dev)
  success:
 //WB add to fill data tcb_desc here. only first fragment is considered, need to change, and you may remove to other place.
 	if (txb) {
-		struct cb_desc *tcb_desc = (struct cb_desc *)(txb->fragments[0]->cb + MAX_DEV_ADDR_SIZE);
+		tcb_desc = (struct cb_desc *)(txb->fragments[0]->cb + MAX_DEV_ADDR_SIZE);
 		tcb_desc->bTxEnableFwCalcDur = 1;
 		if (is_multicast_ether_addr(header.addr1))
 			tcb_desc->bMulticast = 1;