adc: add adc AT close command

Change-Id: Id2ce4cb0b0619b71ea3fa8ad7ca1bd7f0992d1d8
diff --git a/mbtk/mbtk_lib/src/mbtk_adc.c b/mbtk/mbtk_lib/src/mbtk_adc.c
index ddacf39..18f323e 100755
--- a/mbtk/mbtk_lib/src/mbtk_adc.c
+++ b/mbtk/mbtk_lib/src/mbtk_adc.c
@@ -23,9 +23,35 @@
 #define ADC_DEVICE_802 "/sys/devices/soc.0/d4000000.apb/pxa2xx-i2c.2/i2c-2/2-0030/pm802-bat/adc"
 #define ADC_DEVICE_803 "/sys/kernel/debug/adc"
 
-void mbtk_adc_close(void)
+int mbtk_adc_close(void)
 {
-    system("echo 3 > /sys/kernel/debug/adc");
+    int ret = 0;
+    int fd = 0;
+    char adc = '3';
+    //system("echo 3 > /sys/kernel/debug/adc");
+    if(!access(ADC_DEVICE_803, R_OK))
+    {
+        LOGI("DEV:%s", ADC_DEVICE_803);
+        fd = open(ADC_DEVICE_803, O_RDWR|O_CREAT|O_TRUNC, 0644);
+    }
+    else
+    {
+        LOGE("No found ADC devices.");
+        return -1;
+    }
+
+    if(fd < 0) {
+        LOGE("[%s]  file open error\n", __FUNCTION__);
+        return -2;
+    }
+    ret = write(fd, &adc, 1);
+    if (ret < 0) {
+        LOGE("%s: error writing to file!\n", __FUNCTION__);
+        close(fd);
+        return -2;
+    }
+    close(fd);
+    return 0;
 }
 
 int mbtk_adc_get(mbtk_adc_enum channle)