ARM: dts: s3c6410: correct SMDK6410 board compatible

The SMDK6410 DTS was incorrectly called mini6410, probably copy-paste
from FriendlyARM Mini6410 board.

Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Link: https://lore.kernel.org/r/20201117201106.128813-4-krzk@kernel.org