hwc: Change log message for AD feature

If the AD node is not present in the kernel, make the log sound
less fatal and change it to a debug log.

Change-Id: I14adf2df6375d4a2aa012842bda51faf7870ffa5

libhwcomposer/hwc_ad.cpp

@@ -118,7 +118,7 @@ static int adRead() {
         }
         close(adFd);
     } else {
-        ALOGE("%s: Failed to open /sys/class/graphics/fb%d/ad with error %s",
+        ALOGD("%s: /sys/class/graphics/fb%d/ad could not be opened : %s",
                 __func__, wbFbNum, strerror(errno));
     }
     return ret;