libfdt: Fix bug in fdt_subnode_offset_namelen()

[Jon Loeliger]

> There's currently an off-by-one bug in fdt_subnode_offset_namelen()
> which causes it to keep searching after it's finished the subnodes of
> the given parent, and into the subnodes of siblings of the original
> node which come after it in the tree.
> 
> This patch fixes the bug.  It also extends the subnode_offset testcase
> (updating all of the 'test_tree1' example trees in the process) to
> catch it.
> 
> Signed-off-by: David Gibson <david at gibson.dropbear.id.au>

Applied.

Thanks,
jdl