thunderbolt: Remove a meaningless NULL pointer check before dma_pool_destroy

dma_pool_destroy() already takes NULL pointer into account so there is
no need to check that again in tb_ctl_free().
Signed-off-by: zhong jiang <zhongjiang@huawei.com>
[mw: reword commit log a bit]
Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/thunderbolt/ctl.c

@@ -662,8 +662,7 @@ void tb_ctl_free(struct tb_ctl *ctl)
 		tb_ctl_pkg_free(ctl->rx_packets[i]);
 
 
-	if (ctl->frame_pool)
-		dma_pool_destroy(ctl->frame_pool);
+	dma_pool_destroy(ctl->frame_pool);
 	kfree(ctl);
 }