swim3: mark swim3_init() static

This is the module init function, which by definition is used only
locally, so mark it static to avoid a warning:

drivers/block/swim3.c:1280:5: error: no previous prototype for 'swim3_init' [-Werror=missing-prototypes]
Reviewed-by: Jack Wang <jinpu.wang@ionos.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

drivers/block/swim3.c

@@ -1277,7 +1277,7 @@ static struct macio_driver swim3_driver =
 };
 
 
-int swim3_init(void)
+static int swim3_init(void)
 {
 	macio_register_driver(&swim3_driver);
 	return 0;