drm/mipi-dsi: move to_mipi_dsi_device() to use container_of_const()

drm/mipi-dsi: move to_mipi_dsi_device() to use container_of_const()

The driver core is changing to pass some pointers as const, so move
to_mipi_dsi_device() to use container_of_const() to handle this change.

to_mipi_dsi_device() now properly keeps the const-ness of the pointer passed
into it, while as before it could be lost.

Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Maxime Ripard <mripard@kernel.org>
Cc: Thomas Zimmermann <tzimmermann@suse.de>
Cc: David Airlie <airlied@gmail.com>
Cc: Daniel Vetter <daniel@ffwll.ch>
Acked-by: Hans de Goede <hdegoede@redhat.com>
Link: https://lore.kernel.org/r/20230111113018.459199-13-gregkh@linuxfoundation.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>