b43: use temporary rate_index for error checking

The mac80211 rate_index changed to be a u8, so
can't hold the negative error value properly.
Use a temporary variable for error checking.
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/b43/xmit.c

@@ -663,7 +663,7 @@ void b43_rx(struct b43_wldev *dev, struct sk_buff *skb, const void *_rxhdr)
 	u32 uninitialized_var(macstat);
 	u16 chanid;
 	u16 phytype;
-	int padding;
+	int padding, rate_idx;
 
 	memset(&status, 0, sizeof(status));
 
@@ -766,16 +766,17 @@ void b43_rx(struct b43_wldev *dev, struct sk_buff *skb, const void *_rxhdr)
 	}
 
 	if (phystat0 & B43_RX_PHYST0_OFDM)
-		status.rate_idx = b43_plcp_get_bitrate_idx_ofdm(plcp,
+		rate_idx = b43_plcp_get_bitrate_idx_ofdm(plcp,
 						phytype == B43_PHYTYPE_A);
 	else
-		status.rate_idx = b43_plcp_get_bitrate_idx_cck(plcp);
-	if (unlikely(status.rate_idx == -1)) {
+		rate_idx = b43_plcp_get_bitrate_idx_cck(plcp);
+	if (unlikely(rate_idx == -1)) {
 		/* PLCP seems to be corrupted.
 		 * Drop the frame, if we are not interested in corrupted frames. */
 		if (!(dev->wl->filter_flags & FIF_PLCPFAIL))
 			goto drop;
 	}
+	status.rate_idx = rate_idx;
 	status.antenna = !!(phystat0 & B43_RX_PHYST0_ANT);
 
 	/*