libfdt: Fix bugs in fdt_get_path()

[Jon Loeliger]

> The current implementation of fdt_get_path() has a couple of bugs,
> fixed by this patch.
> 
> First, contrary to its documentation, on success it returns the length
> of the node's path, rather than 0.  The testcase is correspondingly
> wrong, and the patch fixes this as well.
> 
> Second, in some circumstances, it will return -FDT_ERR_BADOFFSET
> instead of -FDT_ERR_NOSPACE when given insufficient buffer space.
> Specifically this happens when there is insufficient space even to
> hold the path's second last component.  This behaviour is corrected,
> and the testcase updated to check it.
> 
> Signed-off-by: David Gibson <david at gibson.dropbear.id.au>

Applied.

Thanks,
jdl