of: use correct function prototype for of_overlay_fdt_apply()

When CONFIG_OF_OVERLAY is not enabled the fallback stub for
of_overlay_fdt_apply() does not match the prototype for the case when
CONFIG_OF_OVERLAY is enabled. Update the stub to use the correct
function prototype.

Fixes: 39a751a4 ("of: change overlay apply input data from unflattened to FDT")
Signed-off-by: Chris Packham <chris.packham@alliedtelesis.co.nz>
Reviewed-by: Frank Rowand <frank.rowand@sony.com>
Signed-off-by: Rob Herring <robh@kernel.org>