rtlwifi: rtl8192cu: Fix error in pointer arithmetic

commit 9473ca6e upstream.

An error in calculating the offset in an skb causes the driver to read
essential device info from the wrong locations. The main effect is that
automatic gain calculations are nonsense.
Signed-off-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
Signed-off-by: Larry Finger <Larry.Finger@lwfinger.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

drivers/net/wireless/rtlwifi/rtl8192cu/trx.c

@@ -343,7 +343,8 @@ bool rtl92cu_rx_query_desc(struct ieee80211_hw *hw,
 					(bool)GET_RX_DESC_PAGGR(pdesc));
 	rx_status->mactime = GET_RX_DESC_TSFL(pdesc);
 	if (phystatus) {
-		p_drvinfo = (struct rx_fwinfo_92c *)(pdesc + RTL_RX_DESC_SIZE);
+		p_drvinfo = (struct rx_fwinfo_92c *)(skb->data +
+						     stats->rx_bufshift);
 		rtl92c_translate_rx_signal_stuff(hw, skb, stats, pdesc,
 						 p_drvinfo);
 	}