fix keypad lighting up when screen backlight auto-adjusts

If the screen backlight was already lit and is just changing brightness,
don't blindly illuminate the keypad

Change-Id: If7473eb57aa4d48bc98a4bb42b9becc80764b1f8
Signed-off-by: Gary D <garyd9@gmail.com>

exynos4/exynos4x12/liblights/lights.c

@@ -126,11 +126,15 @@ static int set_light_backlight(struct light_device_t *dev,
             struct light_state_t const *state)
 {
     int err = 0;
+    status int s_previous_brightness = -1;
     int brightness = rgb_to_brightness(state);
 
     pthread_mutex_lock(&g_lock);
     err = write_int(PANEL_FILE, brightness);
-    err = write_int(BUTTON_FILE, brightness > 0 ? 1 : 2);
+    if (!s_previous_brightness && (brightness > 0)) {
+        err = write_int(BUTTON_FILE, brightness > 0 ? 1 : 2);
+        s_previous_brightness = brightness;
+    }
     pthread_mutex_unlock(&g_lock);
 
     return err;