drm/bridge: parade-ps8640: Make sure we drop the AUX mutex in the error case

After commit 26db46b ("drm/bridge: parade-ps8640: Ensure bridge
is suspended in .post_disable()"), if we hit the error case in
ps8640_aux_transfer() then we return without dropping the mutex. Fix
this oversight.

Fixes: 26db46b ("drm/bridge: parade-ps8640: Ensure bridge is suspended in .post_disable()")
Reviewed-by: Hsin-Yi Wang <hsinyi@chromium.org>
Signed-off-by: Douglas Anderson <dianders@chromium.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20240117103502.1.Ib726a0184913925efc7e99c4d4fc801982e1bc24@changeid

Author: dianders

drivers/gpu/drm/bridge/parade-ps8640.c

@@ -351,11 +351,13 @@ static ssize_t ps8640_aux_transfer(struct drm_dp_aux *aux,
 	ret = _ps8640_wait_hpd_asserted(ps_bridge, 200 * 1000);
 	if (ret) {
 		pm_runtime_put_sync_suspend(dev);
-		return ret;
+		goto exit;
 	}
 	ret = ps8640_aux_transfer_msg(aux, msg);
 	pm_runtime_mark_last_busy(dev);
 	pm_runtime_put_autosuspend(dev);
+
+exit:
 	mutex_unlock(&ps_bridge->aux_lock);
 
 	return ret;