of: overlay: Move devicetree_corrupt() check up

There is no point in doing several preparatory steps in
of_overlay_fdt_apply(), only to see of_overlay_apply() return early
because of a corrupt device tree.

Move the check for a corrupt device tree from of_overlay_apply() to
of_overlay_fdt_apply(), to check for this as early as possible.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Frank Rowand <frank.rowand@sony.com>
Tested-by: Frank Rowand <frank.rowand@sony.com>
Signed-off-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/c91ce7112eb5167ea46a43d8a980e76b920010ba.1657893306.git.geert+renesas@glider.be