drm/atomic-helper: fix parameter order in drm_format_conv_state_copy() call

Old and new state parameters are swapped, so the old state was cleared
instead of the new duplicated state.

Fixes: 90367458 ("drm/atomic-helper: Add format-conversion state to shadow-plane state")
Signed-off-by: Lucas Stach <l.stach@pengutronix.de>
Tested-by: Leonard Göhrs <l.goehrs@pengutronix.de>
Reviewed-by: Thomas Zimmermann <tzimmermann@suse.de>
Cc: <stable@vger.kernel.org> # v6.8+
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20240404081756.2714424-1-l.stach@pengutronix.de

drivers/gpu/drm/drm_gem_atomic_helper.c

@@ -224,8 +224,8 @@ __drm_gem_duplicate_shadow_plane_state(struct drm_plane *plane,
 
 	__drm_atomic_helper_plane_duplicate_state(plane, &new_shadow_plane_state->base);
 
-	drm_format_conv_state_copy(&shadow_plane_state->fmtcnv_state,
-				   &new_shadow_plane_state->fmtcnv_state);
+	drm_format_conv_state_copy(&new_shadow_plane_state->fmtcnv_state,
+				   &shadow_plane_state->fmtcnv_state);
 }
 EXPORT_SYMBOL(__drm_gem_duplicate_shadow_plane_state);