fdt_fixups: relocate the /chosen node after applying fixups

As indicated by the comment, any fixups applied (which might include
overlays) can invalidate the previously located node by adding nodes or
setting/adding properties. The later fdt_setprop of fixup-applied property
would then fail because of the bad/wrong node offset.

This would have generally been harmless, but potentially caused multiple
applications of fixups and caused a little bit of bloat.

MFC after: 1 week