Fix logging image spaces.

Fix an error introduced by
    https://android-review.googlesource.com/833352 .

Test: m
Bug: 176155658
Change-Id: Ibb48674165ffb4a9a465865d6728661c1fb5340d
diff --git a/runtime/gc/space/image_space.cc b/runtime/gc/space/image_space.cc
index 99aee0b..8bfb053 100644
--- a/runtime/gc/space/image_space.cc
+++ b/runtime/gc/space/image_space.cc
@@ -3234,7 +3234,7 @@
 
   if (VLOG_IS_ON(image)) {
     LOG(INFO) << "ImageSpace::BootImageLoader::LoadFromSystem exiting "
-        << boot_image_spaces->front();
+        << *boot_image_spaces->front();
     logger.Dump(LOG_STREAM(INFO));
   }
   return true;
@@ -3264,7 +3264,7 @@
 
   if (VLOG_IS_ON(image)) {
     LOG(INFO) << "ImageSpace::BootImageLoader::LoadFromDalvikCache exiting "
-        << boot_image_spaces->front();
+        << *boot_image_spaces->front();
     logger.Dump(LOG_STREAM(INFO));
   }
   return true;