image_burner: USE scoped_ptr<char[]> for array.

I saw  ERROR: AddressSanitizer: alloc-dealloc-mismatch (operator new [] vs operator delete)
on 0x600400001e90 when running ASan with it.
This patch fix this problem.

BUG=None
TEST=FEATURES="test" emerge-lumpy chromeos-imageburner

Change-Id: Ia55570cbe9400e855a67a797509039bcba5c3c6d
Reviewed-on: https://gerrit.chromium.org/gerrit/61747
Reviewed-by: Toni Barzic <tbarzic@chromium.org>
Commit-Queue: Yunlian Jiang <yunlian@chromium.org>
Tested-by: Yunlian Jiang <yunlian@chromium.org>
diff --git a/image_burner_impl.cc b/image_burner_impl.cc
index bc6f856..f8ffc12 100644
--- a/image_burner_impl.cc
+++ b/image_burner_impl.cc
@@ -117,7 +117,7 @@
   }
 
   if (success) {
-    scoped_ptr<char> buffer(new char[data_block_size_]);
+    scoped_ptr<char[]> buffer(new char[data_block_size_]);
 
     int64 total_burnt = 0;
     int64 image_size = reader_->GetSize();