mips: Loongson: Fix the link time qualifier of 'serial_exit()'

'exit' functions should be marked as __exit, not __init.

Fixes: 85cc0288 ("mips: make loongsoon serial driver explicitly modular")
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Signed-off-by: Paul Burton <paul.burton@mips.com>
Cc: chenhc@lemote.com
Cc: ralf@linux-mips.org
Cc: jhogan@kernel.org
Cc: linux-mips@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Cc: kernel-janitors@vger.kernel.org

arch/mips/loongson64/common/serial.c

@@ -110,7 +110,7 @@ static int __init serial_init(void)
 }
 module_init(serial_init);
 
-static void __init serial_exit(void)
+static void __exit serial_exit(void)
 {
 	platform_device_unregister(&uart8250_device);
 }