CHROMIUM: verity: add BUG in check_block for consistency with verify_path
We assume that the caller guarantees that all nodes along the path are
already populated. We already have a BUG_ON checking this in verify_path.
This change adds a similar BUG_ON in check_path and removes the code
which checks the entry state.
TEST=Ran unit tests in dm-verity.git. Ran platform_DMVerityCorruption on H/W.
Signed-off-by: Mandeep Singh Baines <email@example.com>