staging: fbtft: Fix error path in fbtft_driver_module_init()

If registering the platform driver fails, the function must not return
without undoing the spi driver registration first.

Fixes: c296d5f ("staging: fbtft: core support")
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Link: https://lore.kernel.org/r/20220118181338.207943-1-u.kleine-koenig@pengutronix.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: Uwe Kleine-König

drivers/staging/fbtft/fbtft.h

@@ -334,7 +334,10 @@ static int __init fbtft_driver_module_init(void)                           \
 	ret = spi_register_driver(&fbtft_driver_spi_driver);               \
 	if (ret < 0)                                                       \
 		return ret;                                                \
-	return platform_driver_register(&fbtft_driver_platform_driver);    \
+	ret = platform_driver_register(&fbtft_driver_platform_driver);     \
+	if (ret < 0)                                                       \
+		spi_unregister_driver(&fbtft_driver_spi_driver);           \
+	return ret;                                                        \
 }                                                                          \
 									   \
 static void __exit fbtft_driver_module_exit(void)                          \