drm/ssd130x: Use shadow-buffer helpers when managing plane's state

The commit 45b58669 ("drm/ssd130x: Allocate buffer in the plane's
.atomic_check() callback") moved the buffers allocation to be done in
the primary plane's .atomic_check() callback.

But it missed that since the driver uses a shadow-buffered plane, the
__drm_gem_{reset,duplicate,destroy}_shadow_plane() helper functions
must be used in the struct drm_plane_funcs handlers.

This was missed because the mentioned commit did not remove the macro
DRM_GEM_SHADOW_PLANE_FUNCS, which leads to the custom plane's atomic
state management handlers to not be used.

Fixes: 45b58669 ("drm/ssd130x: Allocate buffer in the plane's .atomic_check() callback")
Reported-by: Arnd Bergmann <arnd@arndb.de>
Closes: https://lore.kernel.org/dri-devel/20230727122412.2464210-1-arnd@kernel.org


Suggested-by: Thomas Zimmermann <tzimmermann@suse.de>
Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>
Reviewed-by: Thomas Zimmermann <tzimmermann@suse.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20230727140453.577445-1-javierm@redhat.com