drm/ssd130x: Call drm_atomic_helper_shutdown() at remove time

Based on grepping through the source code, this driver appears to be
missing a call to drm_atomic_helper_shutdown() at remove time. Let's
add it.

The fact that we should call drm_atomic_helper_shutdown() in the case
of OS driver remove comes straight out of the kernel doc "driver
instance overview" in drm_drv.c.
Suggested-by: Maxime Ripard <mripard@kernel.org>
Acked-by: Maxime Ripard <mripard@kernel.org>
Signed-off-by: Douglas Anderson <dianders@chromium.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20230901163944.RFT.4.I4752a39ad9f8fd08b32c2b78a8a3e40491bfb5eb@changeid

drivers/gpu/drm/solomon/ssd130x.c

@@ -1245,6 +1245,7 @@ EXPORT_SYMBOL_GPL(ssd130x_probe);
 void ssd130x_remove(struct ssd130x_device *ssd130x)
 {
 	drm_dev_unplug(&ssd130x->drm);
+	drm_atomic_helper_shutdown(&ssd130x->drm);
 }
 EXPORT_SYMBOL_GPL(ssd130x_remove);