platform: generic: Make use of fdt_match_node()

It makes sense to use fdt_match_node() instead of fdt_find_match()
in fw_platform_lookup_special() as we already have the start offset
to search from.

Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Reviewed-by: Anup Patel <anup@brainfault.org>