rt2800lib: fix wrong -128dBm when signal is stronger than -12dBm

This patch correct the type of variables containing the rssi
values read from the rxwi.

In function rt2800_agc_to_rssi() 3 variables (rssi0, rssi1, rss2)
defined as int was assigned a 16bit signed values as unsigned.
From a test with a hi-gain antenna I verified that the rxwi
contains signed rssi values in the  range -13/+81 (inclusive)
with 0 as an error condition. In case of negative values a
condition is triggered and the function return -128dBm while
the signal is at its maximum. This patch correct the cast so
negative values are not treated as very high positive values
(ex. -13 does not become 243).

Signed-off-by: Luigi Tarenga <luigi.tarenga@gmail.com>
Reviewed-by: Stanislaw Gruszka <sgruszka@redhat.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/rt2x00/rt2800lib.c

@@ -514,9 +514,9 @@ EXPORT_SYMBOL_GPL(rt2800_write_tx_data);
 
 static int rt2800_agc_to_rssi(struct rt2x00_dev *rt2x00dev, u32 rxwi_w2)
 {
-	int rssi0 = rt2x00_get_field32(rxwi_w2, RXWI_W2_RSSI0);
-	int rssi1 = rt2x00_get_field32(rxwi_w2, RXWI_W2_RSSI1);
-	int rssi2 = rt2x00_get_field32(rxwi_w2, RXWI_W2_RSSI2);
+	s8 rssi0 = rt2x00_get_field32(rxwi_w2, RXWI_W2_RSSI0);
+	s8 rssi1 = rt2x00_get_field32(rxwi_w2, RXWI_W2_RSSI1);
+	s8 rssi2 = rt2x00_get_field32(rxwi_w2, RXWI_W2_RSSI2);
 	u16 eeprom;
 	u8 offset0;
 	u8 offset1;
@@ -552,7 +552,7 @@ static int rt2800_agc_to_rssi(struct rt2x00_dev *rt2x00dev, u32 rxwi_w2)
 	 * which gives less energy...
 	 */
 	rssi0 = max(rssi0, rssi1);
-	return max(rssi0, rssi2);
+	return (int)max(rssi0, rssi2);
 }
 
 void rt2800_process_rxwi(struct queue_entry *entry,