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>
1 file changed