rc80211-pid: simplify and fix shift_adjust

Simplify and fix rate_control_pid_shift_adjust(). A bug prevented correct
mapping of sorted rates, and readability was seriously flawed.
Signed-off-by: Stefano Brivio <stefano.brivio@polimi.it>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/mac80211/rc80211_pid_algo.c

@@ -74,29 +74,27 @@ static int rate_control_pid_shift_adjust(struct rc_pid_rateinfo *r,
 {
 	int i, j, k, tmp;
 
-	if (cur + adj < 0)
-		return 0;
-	if (cur + adj >= l)
-		return l - 1;
+	j = r[cur].rev_index;
+	i = j + adj;
 
-	i = r[cur + adj].rev_index;
+	if (i < 0)
+		return r[0].index;
+	if (i >= l - 1)
+		return r[l - 1].index;
 
-	j = r[cur].rev_index;
+	tmp = i;
 
 	if (adj < 0) {
-			tmp = i;
 		for (k = j; k >= i; k--)
 			if (r[k].diff <= r[j].diff)
 				tmp = k;
-			return r[tmp].index;
-	} else if (adj > 0) {
-			tmp = i;
+	} else {
 		for (k = i + 1; k + i < l; k++)
 			if (r[k].diff <= r[i].diff)
 				tmp = k;
-			return r[tmp].index;
 	}
-	return cur + adj;
+
+	return r[tmp].index;
 }
 
 static void rate_control_pid_adjust_rate(struct ieee80211_local *local,