verity: remove the depth parameter from bht_create

We want to only support regular tries with a single root hash block.

BUG=chromium-os9752
TEST=Ran dm-verity.git unit tests. Ran platform_DMVerityCorruption on H/W.

Change-Id: I49a8b74b8343c4cb5aa871a81b45f06025fe1011

R=wad@chromium.org,taysom@chromium.org,ups@chromium.org

Review URL: http://codereview.chromium.org/6811030
6 files changed