rt2x00: rt2800lib: fix VGC programming for RT3572 and RT3593

According to the DPO_RT5572_LinuxSTA_2.6.1.3_20121022
reference driver, programming of the 'BBP 66' register
on the RT3572 and RT3593 chipsets must be done via the
'rt2800_bbp_write_with_rx_chain' function. This ensures
that value is correclty set for all RX chains.

References:
  RT35xx_ChipAGCAdjust and RT35xx_SetAGCInitValue functions
  in chips/rt35xx.c
Signed-off-by: Gabor Juhos <juhosg@openwrt.org>
Acked-by: Stanislaw Gruszka <stf_xl@wp.pl>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/rt2x00/rt2800lib.c

@@ -4442,11 +4442,17 @@ static inline void rt2800_set_vgc(struct rt2x00_dev *rt2x00dev,
 				  struct link_qual *qual, u8 vgc_level)
 {
 	if (qual->vgc_level != vgc_level) {
-		if (rt2x00_rt(rt2x00dev, RT5592)) {
+		if (rt2x00_rt(rt2x00dev, RT3572) ||
+		    rt2x00_rt(rt2x00dev, RT3593)) {
+			rt2800_bbp_write_with_rx_chain(rt2x00dev, 66,
+						       vgc_level);
+		} else if (rt2x00_rt(rt2x00dev, RT5592)) {
 			rt2800_bbp_write(rt2x00dev, 83, qual->rssi > -65 ? 0x4a : 0x7a);
 			rt2800_bbp_write_with_rx_chain(rt2x00dev, 66, vgc_level);
-		} else
+		} else {
 			rt2800_bbp_write(rt2x00dev, 66, vgc_level);
+		}
+
 		qual->vgc_level = vgc_level;
 		qual->vgc_level_reg = vgc_level;
 	}