verity: root hash should not rely on uninitialized memory

Fixes a valgrind warning. This bug is harmless should so
not be considered critical.

BUG=chromium-os:9752
TEST=Ran dm-verity.git unit tests with USE=valgrind.

Change-Id: I689bbf493e7fe073980c3a0ee6df8c2a6dbd4620
Reviewed-on: http://gerrit.chromium.org/gerrit/4338
Reviewed-by: Paul Taysom <taysom@google.com>
Reviewed-by: Will Drewry <wad@chromium.org>
Tested-by: Mandeep Singh Baines <msb@chromium.org>
2 files changed