ath5k: correct channel setting for 2.5 mhz spacing

These channels aren't selectable anyway, but our calculations
for 2.5 mhz frequencies are incorrect.  The value is supposed to
be:

  (frequency - reference) * (10/25)

i.e., divide by 2.5, but we were instead doing:

  (10 * frequency - reference) / 25.

Additionally, the check for (frequency % 5 == 2) had an extra
subtraction that wasn't in madwifi HAL.

Signed-off-by: Bob Copeland <me@bobcopeland.com>
Acked-by: Bruno Randolf <br1@einfach.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/ath/ath5k/phy.c

@@ -979,7 +979,7 @@ static int ath5k_hw_rf5112_channel(struct ath5k_hw *ah,
 			return -EINVAL;
 
 		data0 = ath5k_hw_bitswap((data0 << 2) & 0xff, 8);
-	} else if ((c - (c % 5)) != 2 || c > 5435) {
+	} else if ((c % 5) != 2 || c > 5435) {
 		if (!(c % 20) && c >= 5120) {
 			data0 = ath5k_hw_bitswap(((c - 4800) / 20 << 2), 8);
 			data2 = ath5k_hw_bitswap(3, 2);
@@ -992,7 +992,7 @@ static int ath5k_hw_rf5112_channel(struct ath5k_hw *ah,
 		} else
 			return -EINVAL;
 	} else {
-		data0 = ath5k_hw_bitswap((10 * (c - 2) - 4800) / 25 + 1, 8);
+		data0 = ath5k_hw_bitswap((10 * (c - 2 - 4800)) / 25 + 1, 8);
 		data2 = ath5k_hw_bitswap(0, 2);
 	}
 
@@ -1020,7 +1020,7 @@ static int ath5k_hw_rf2425_channel(struct ath5k_hw *ah,
 		data0 = ath5k_hw_bitswap((c - 2272), 8);
 		data2 = 0;
 	/* ? 5GHz ? */
-	} else if ((c - (c % 5)) != 2 || c > 5435) {
+	} else if ((c % 5) != 2 || c > 5435) {
 		if (!(c % 20) && c < 5120)
 			data0 = ath5k_hw_bitswap(((c - 4800) / 20 << 2), 8);
 		else if (!(c % 10))
@@ -1031,7 +1031,7 @@ static int ath5k_hw_rf2425_channel(struct ath5k_hw *ah,
 			return -EINVAL;
 		data2 = ath5k_hw_bitswap(1, 2);
 	} else {
-		data0 = ath5k_hw_bitswap((10 * (c - 2) - 4800) / 25 + 1, 8);
+		data0 = ath5k_hw_bitswap((10 * (c - 2 - 4800)) / 25 + 1, 8);
 		data2 = ath5k_hw_bitswap(0, 2);
 	}