moxart: fix potential use-after-free on remove path

It was reported that the mmc host structure could be accessed after it
was freed in moxart_remove(), so fix this by saving the base register of
the device and using it instead of the pointer dereference.

Cc: Ulf Hansson <ulf.hansson@linaro.org>
Cc: Xiyu Yang <xiyuyang19@fudan.edu.cn>
Cc: Xin Xiong <xiongx18@fudan.edu.cn>
Cc: Xin Tan <tanxin.ctf@gmail.com>
Cc: Tony Lindgren <tony@atomide.com>
Cc: Yang Li <yang.lee@linux.alibaba.com>
Cc: linux-mmc@vger.kernel.org
Cc: stable <stable@vger.kernel.org>
Reported-by: whitehat002 <hackyzh002@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Link: https://lore.kernel.org/r/20220127071638.4057899-1-gregkh@linuxfoundation.org
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>

Author: gregkh

drivers/mmc/host/moxart-mmc.c

@@ -705,12 +705,12 @@ static int moxart_remove(struct platform_device *pdev)
 	if (!IS_ERR_OR_NULL(host->dma_chan_rx))
 		dma_release_channel(host->dma_chan_rx);
 	mmc_remove_host(mmc);
-	mmc_free_host(mmc);
 
 	writel(0, host->base + REG_INTERRUPT_MASK);
 	writel(0, host->base + REG_POWER_CONTROL);
 	writel(readl(host->base + REG_CLOCK_CONTROL) | CLK_OFF,
 	       host->base + REG_CLOCK_CONTROL);
+	mmc_free_host(mmc);
 
 	return 0;
 }