ttyprintk: Allow built as a module

The driver is well written to be used as a module, just the exit call
is missing.
Reviewed-by: NJean Delvare <jdelvare@suse.de>
Signed-off-by: NTakashi Iwai <tiwai@suse.de>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/char/Kconfig

@@ -40,7 +40,7 @@ config SGI_MBCS
 source "drivers/tty/serial/Kconfig"
 
 config TTY_PRINTK
-	bool "TTY driver to output user messages via printk"
+	tristate "TTY driver to output user messages via printk"
 	depends on EXPERT && TTY
 	default n
 	---help---

drivers/char/ttyprintk.c

@@ -17,7 +17,7 @@
 #include <linux/device.h>
 #include <linux/serial.h>
 #include <linux/tty.h>
-#include <linux/export.h>
+#include <linux/module.h>
 
 struct ttyprintk_port {
 	struct tty_port port;
@@ -214,4 +214,15 @@ static int __init ttyprintk_init(void)
 	tty_port_destroy(&tpk_port.port);
 	return ret;
 }
+
+static void __exit ttyprintk_exit(void)
+{
+	tty_unregister_driver(ttyprintk_driver);
+	put_tty_driver(ttyprintk_driver);
+	tty_port_destroy(&tpk_port.port);
+}
+
 device_initcall(ttyprintk_init);
+module_exit(ttyprintk_exit);
+
+MODULE_LICENSE("GPL");