spi: tegra20-slink: fix UAF in tegra_slink_remove()

After calling spi_unregister_master(), the refcount of master will
be decrease to 0, and it will be freed in spi_controller_release(),
the device data also will be freed, so it will lead a UAF when using
'tspi'. To fix this, get the master before unregister and put it when
finish using it.

Fixes: 26c86341 ("spi: tegra20-slink: Don't use resource-managed spi_register helper")
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>
Link: https://lore.kernel.org/r/20220713094024.1508869-1-yangyingliang@huawei.comSigned-off-by: Mark Brown <broonie@kernel.org>

drivers/spi/spi-tegra20-slink.c

@@ -1136,7 +1136,7 @@ static int tegra_slink_probe(struct platform_device *pdev)
 
 static int tegra_slink_remove(struct platform_device *pdev)
 {
-	struct spi_master *master = platform_get_drvdata(pdev);
+	struct spi_master *master = spi_master_get(platform_get_drvdata(pdev));
 	struct tegra_slink_data	*tspi = spi_master_get_devdata(master);
 
 	spi_unregister_master(master);
@@ -1151,6 +1151,7 @@ static int tegra_slink_remove(struct platform_device *pdev)
 	if (tspi->rx_dma_chan)
 		tegra_slink_deinit_dma_param(tspi, true);
 
+	spi_master_put(master);
 	return 0;
 }