media: platform: exynos4-is: Fix error handling in fimc_md_init()

A problem about modprobe s5p_fimc failed is triggered with the
following log given:

 [  272.075275] Error: Driver 'exynos4-fimc' is already registered, aborting...
 modprobe: ERROR: could not insert 's5p_fimc': Device or resource busy

The reason is that fimc_md_init() returns platform_driver_register()
directly without checking its return value, if platform_driver_register()
failed, it returns without unregister fimc_driver, resulting the
s5p_fimc can never be installed later.
A simple call graph is shown as below:

 fimc_md_init()
   fimc_register_driver() # register fimc_driver
   platform_driver_register()
     platform_driver_register()
       driver_register()
         bus_add_driver()
           dev = kzalloc(...) # OOM happened
   # return without unregister fimc_driver

Fix by unregister fimc_driver when platform_driver_register() returns
error.

Fixes: d3953223 ("[media] s5p-fimc: Add the media device driver")
Signed-off-by: Yuan Can <yuancan@huawei.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>

drivers/media/platform/samsung/exynos4-is/fimc-core.c

@@ -1173,7 +1173,7 @@ int __init fimc_register_driver(void)
 	return platform_driver_register(&fimc_driver);
 }
 
-void __exit fimc_unregister_driver(void)
+void fimc_unregister_driver(void)
 {
 	platform_driver_unregister(&fimc_driver);
 }

drivers/media/platform/samsung/exynos4-is/media-dev.c

@@ -1584,7 +1584,11 @@ static int __init fimc_md_init(void)
 	if (ret)
 		return ret;
 
-	return platform_driver_register(&fimc_md_driver);
+	ret = platform_driver_register(&fimc_md_driver);
+	if (ret)
+		fimc_unregister_driver();
+
+	return ret;
 }
 
 static void __exit fimc_md_exit(void)