drm/stm: ltdc: unify log system

DRM_ERROR and similar are deprecated.  Use drm_dev based logging.

Link: https://lore.kernel.org/r/[email protected]
Acked-by: Yannick Fertre <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Raphael Gallais-Pou <[email protected]>

Author: rgallaispouSTM