spi: rpc-if: Fix use-after-free on unbind

rpcif_spi_remove() accesses the driver's private data after calling
spi_unregister_controller() even though that function releases the last
reference on the spi_controller and thereby frees the private data.

Fix by switching over to the new devm_spi_alloc_master() helper which
keeps the private data accessible until the driver has unbound.

Fixes: eb8d6d46 ("spi: add Renesas RPC-IF driver")
Signed-off-by: Lukas Wunner <lukas@wunner.de>
Cc: <stable@vger.kernel.org> # v5.9+: 5e844cc3: spi: Introduce device-managed SPI controller allocation
Cc: <stable@vger.kernel.org> # v5.9+
Cc: Sergei Shtylyov <s.shtylyov@omprussia.ru>
Link: https://lore.kernel.org/r/c5da472c28021da2f6517441685cef033d40b140.1607286887.git.lukas@wunner.deSigned-off-by: Mark Brown <broonie@kernel.org>

drivers/spi/spi-rpc-if.c

@@ -134,7 +134,7 @@ static int rpcif_spi_probe(struct platform_device *pdev)
 	struct rpcif *rpc;
 	int error;
 
-	ctlr = spi_alloc_master(&pdev->dev, sizeof(*rpc));
+	ctlr = devm_spi_alloc_master(&pdev->dev, sizeof(*rpc));
 	if (!ctlr)
 		return -ENOMEM;
 
@@ -159,13 +159,8 @@ static int rpcif_spi_probe(struct platform_device *pdev)
 	error = spi_register_controller(ctlr);
 	if (error) {
 		dev_err(&pdev->dev, "spi_register_controller failed\n");
-		goto err_put_ctlr;
-	}
-	return 0;
-
-err_put_ctlr:
 		rpcif_disable_rpm(rpc);
-	spi_controller_put(ctlr);
+	}
 
 	return error;
 }