rt2x00: rt2800lib: fix frequency offset boundary calculation

The current code in the 'rt2800_adjust_freq_offset'
function limits the device specific frequency offset
value to FREQ_BOUND but ignores the fact that the
uppermost bit is not part of the frequency offset
value. As the result, the driver always uses the
FREQ_BOUND value if the uppermost bit is set.

Update the code to use the correct source value
for calculating the boundary.

Based on the DPO_RT5572_LinuxSTA_2.6.0.1_20120629
driver.

Reference:
  RTMPAdjustFrequencyOffset function in common/rt_rf.c
Signed-off-by: Gabor Juhos <juhosg@openwrt.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/rt2x00/rt2800lib.c

@@ -2496,13 +2496,14 @@ static void rt2800_config_channel_rf3053(struct rt2x00_dev *rt2x00dev,
 
 static void rt2800_adjust_freq_offset(struct rt2x00_dev *rt2x00dev)
 {
+	u8 freq_offset;
 	u8 rfcsr;
 
+	freq_offset = rt2x00_get_field8(rt2x00dev->freq_offset, RFCSR17_CODE);
+	freq_offset = min_t(u8, freq_offset, FREQ_OFFSET_BOUND);
+
 	rt2800_rfcsr_read(rt2x00dev, 17, &rfcsr);
-	if (rt2x00dev->freq_offset > FREQ_OFFSET_BOUND)
-		rt2x00_set_field8(&rfcsr, RFCSR17_CODE, FREQ_OFFSET_BOUND);
-	else
-		rt2x00_set_field8(&rfcsr, RFCSR17_CODE, rt2x00dev->freq_offset);
+	rt2x00_set_field8(&rfcsr, RFCSR17_CODE, freq_offset);
 	rt2800_rfcsr_write(rt2x00dev, 17, rfcsr);
 }