Fix a log issue in ui.cpp.

It's a copy/paste error when addressing reviewer's comment for commit
6278bdf3490a2f6682f5a9c47350b3d9f92a9165.

Test: recovery gives the right message (e.g. "Permission denied") when
      it fails to read max_brightness.

Change-Id: I10372c82595bdc00a6f6725f036c02721b19a1aa
diff --git a/ui.cpp b/ui.cpp
index 5efdc5a..3ecd6d1 100644
--- a/ui.cpp
+++ b/ui.cpp
@@ -100,7 +100,7 @@
   // we don't have a good way to query the default value.
   std::string content;
   if (!android::base::ReadFileToString(MAX_BRIGHTNESS_FILE, &content)) {
-    LOG(WARNING) << "Failed to read max brightness: " << content;
+    PLOG(WARNING) << "Failed to read max brightness";
     return false;
   }