staging: rtl8192u: ieee80211: Fix incorrect type in assignment

Added le16_to_cpu() conversion fixing the following warning in assignment detected by sparse:

drivers/staging/rtl8192u/ieee80211/ieee80211_softmac.c:2157:30: warning: invalid assignment: +=
drivers/staging/rtl8192u/ieee80211/ieee80211_softmac.c:2157:30:    left side has type unsigned long
drivers/staging/rtl8192u/ieee80211/ieee80211_softmac.c:2157:30:    right side has type restricted __le16

Signed-off-by: Gaston Gonzalez <gascoar@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/rtl8192u/ieee80211/ieee80211_softmac.c

@@ -2154,7 +2154,7 @@ void ieee80211_softmac_xmit(struct ieee80211_txb *txb, struct ieee80211_device *
 	ieee80211_sta_wakeup(ieee, 0);
 
 	/* update the tx status */
-	ieee->stats.tx_bytes += txb->payload_size;
+	ieee->stats.tx_bytes += le16_to_cpu(txb->payload_size);
 	ieee->stats.tx_packets++;
 	tcb_desc = (cb_desc *)(txb->fragments[0]->cb + MAX_DEV_ADDR_SIZE);
 	if (tcb_desc->bMulticast) {