drm/mgag200: Use offset-adjusted shadow-plane mappings

For framebuffers with non-zero offset fields, shadow-plane helpers
provide a pointer to the first byte of the contained data. Use it in
mgag200.
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Acked-by: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20210803125928.27780-6-tzimmermann@suse.de

drivers/gpu/drm/mgag200/mgag200_mode.c

@@ -898,7 +898,7 @@ mgag200_simple_display_pipe_enable(struct drm_simple_display_pipe *pipe,
 	mga_crtc_load_lut(crtc);
 	mgag200_enable_display(mdev);
 
-	mgag200_handle_damage(mdev, fb, &fullscreen, &shadow_plane_state->map[0]);
+	mgag200_handle_damage(mdev, fb, &fullscreen, &shadow_plane_state->data[0]);
 }
 
 static void
@@ -959,7 +959,7 @@ mgag200_simple_display_pipe_update(struct drm_simple_display_pipe *pipe,
 		return;
 
 	if (drm_atomic_helper_damage_merged(old_state, state, &damage))
-		mgag200_handle_damage(mdev, fb, &damage, &shadow_plane_state->map[0]);
+		mgag200_handle_damage(mdev, fb, &damage, &shadow_plane_state->data[0]);
 }
 
 static struct drm_crtc_state *