dtc: Fix uninitialized use of structure_ok

[Jon Loeliger]

So, like, the other day David Gibson mumbled:
> My rework of the tree checking code introduced a potentially nasty bug
> - it uses the structure_ok variable uninitialized.  This patch fixes
> the problem.  It's a fairly ugly bandaid approach, but the ugly will
> disappear once future patches have folded the semantic checks into the
> new framework.
> 
> Signed-off-by: David Gibson <david at gibson.dropbear.id.au>

Applied.

Thanks!
jdl