libfdt: Fix handling of trailing / in fdt_path_offset()

[Jon Loeliger]

So, like, the other day David Gibson mumbled:
> Currently, fdt_path_offset() returns FDL_ERR_BADOFFSET if given a path
> with a trailing '/'.  In particular this means that
> fdt_path_offset("/") returns FDT_ERR_BADOFFSET rather than 0 as one
> would expect.
> 
> This patch fixes the function to accept and ignore trailing '/'
> characters.  As well as allowing fdt_path_offset("/") this means that
> fdt_path_offset("/foo/") will return the same as
> fdt_path_offset("/foo") which seems in keeping with the principle of
> least surprise.
> 
> This also adds a testcase to ensure that fdt_path_offset("/") returns
> 0 as it should.
> 
> Signed-off-by: David Gibson <david at gibson.dropbear.id.au>

Applied.

Thanks,
jdl