spi: spi-axi: fix potential use-after-free after deregistration

Take an extra reference to the controller before deregistering it to
prevent use-after-free in the interrupt handler in case an interrupt
fires before the line is disabled.

Fixes: b1353d1c ("spi: Add Analog Devices AXI SPI Engine controller support")
Acked-by: NLars-Peter Clausen <lars@metafoo.de>
Signed-off-by: NJohan Hovold <johan@kernel.org>
Signed-off-by: NMark Brown <broonie@kernel.org>

drivers/spi/spi-axi-spi-engine.c

@@ -553,7 +553,7 @@ static int spi_engine_probe(struct platform_device *pdev)
 
 static int spi_engine_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 spi_engine *spi_engine = spi_master_get_devdata(master);
 	int irq = platform_get_irq(pdev, 0);
 
@@ -561,6 +561,8 @@ static int spi_engine_remove(struct platform_device *pdev)
 
 	free_irq(irq, master);
 
+	spi_master_put(master);
+
 	writel_relaxed(0xff, spi_engine->base + SPI_ENGINE_REG_INT_PENDING);
 	writel_relaxed(0x00, spi_engine->base + SPI_ENGINE_REG_INT_ENABLE);
 	writel_relaxed(0x01, spi_engine->base + SPI_ENGINE_REG_RESET);