drm/stm: ltdc: remove error message about scaling

Remove error message about scaling & replace it by a debug
message to avoid too much error.

Signed-off-by: Yannick Fertre <yannick.fertre@foss.st.com>
Acked-by: Raphael Gallais-Pou <raphael.gallais-pou@foss.st.com>
Signed-off-by: Philippe Cornu <philippe.cornu@foss.st.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220603134250.592408-1-yannick.fertre@foss.st.com