exynos4212 liblights: fix keypad lighting up when screen backlight auto-adjusts

clone of http://review.cyanogenmod.com/#/c/18372/

becomes relevant when these are applied:
smdk4210 kernel: cypress touchkey led_timeout functionality (1/2)
http://review.cyanogenmod.com/#/c/18357/
galaxys2/i777: configurable touchkey backlight timeout (2/2)
http://review.cyanogenmod.com/#/c/18431/

Change-Id: I3d4df6574cdd3c6317199a884ef7ac72cb4c71a3

exynos4/exynos4210/liblights/lights.c

@@ -231,17 +231,18 @@ static int
 set_light_backlight(struct light_device_t* dev,
         struct light_state_t const* state)
 {
-        load_settings();
-
     int err = 0;
+    static int s_previous_brightness = -1;
     int brightness = rgb_to_brightness(state);
 
     pthread_mutex_lock(&g_lock);
     err = write_int(PANEL_FILE, brightness);
 
 #ifndef EXYNOS4210_TABLET
-    if (g_enable_touchlight == -1 || g_enable_touchlight > 0)
-        err = write_int(BUTTON_FILE, brightness > 0 ? 1 : 0);
+    if (!s_previous_brightness && (brightness > 0)) {
+        err = write_int(BUTTON_FILE, brightness > 0 ? 1 : 2);
+        s_previous_brightness = brightness;
+    }
 #endif
 
     pthread_mutex_unlock(&g_lock);