drm/solomon: Use drm_WARN_ON_ONCE instead of WARN_ON

drm/solomon: Use drm_WARN_ON_ONCE instead of WARN_ON

To prevent log spam, convert all instances to the DRM-specific
drm_WARN_ON_ONCE() macro. This ensures that a warning is emitted only
the first time the condition is met for a given device instance, which
is the desired behavior within the graphics subsystem.

Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>
Reviewed-by: Thomas Zimmermann <tzimmermann@suse.de>
Signed-off-by: Iker Pedrosa <ikerpedrosam@gmail.com>
Link: https://lore.kernel.org/r/20250920-improve-ssd130x-v2-2-77721e87ae08@gmail.com
Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>