rt2800: 5592: initialize BBP_R138 register

Based on:
RT5592LoadRFNormalModeSetup()

from:
DPO_RT5572_LinuxSTA_2.6.1.3_20121022/chips/rt5592.c

Signed-off-by: Stanislaw Gruszka <stf_xl@wp.pl>
Tested-by: Wanlong Gao <gaowanlong@cn.fujitsu.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/rt2x00/rt2800lib.c

@@ -4859,7 +4859,8 @@ static int rt2800_init_rfcsr(struct rt2x00_dev *rt2x00dev)
 		rt2800_rfcsr_write(rt2x00dev, 17, rfcsr);
 	}
 
-	if (rt2x00_rt(rt2x00dev, RT3090)) {
+	if (rt2x00_rt(rt2x00dev, RT3090) ||
+	    rt2x00_rt(rt2x00dev, RT5592)) {
 		rt2800_bbp_read(rt2x00dev, 138, &bbp);
 
 		/*  Turn off unused DAC1 and ADC1 to reduce power consumption */