USB: console: add dummy __module_get

Add call to __module_get when initialising the fake tty in
usb_console_setup to match the module_put in release_one_tty.

Note that the tty-driver (i.e. usb-serial core) must be compiled-in to
enable the usb console so the __module_get is essentially a noop as
driver->owner will be null.
Reported-by: Ben Hutchings <ben@decadent.org.uk>
Signed-off-by: Johan Hovold <johan@kernel.org>

drivers/usb/serial/console.c

@@ -14,6 +14,7 @@
 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
 
 #include <linux/kernel.h>
+#include <linux/module.h>
 #include <linux/slab.h>
 #include <linux/tty.h>
 #include <linux/console.h>
@@ -144,6 +145,7 @@ static int usb_console_setup(struct console *co, char *options)
 			init_ldsem(&tty->ldisc_sem);
 			INIT_LIST_HEAD(&tty->tty_files);
 			kref_get(&tty->driver->kref);
+			__module_get(tty->driver->owner);
 			tty->ops = &usb_console_fake_tty_ops;
 			if (tty_init_termios(tty)) {
 				retval = -ENOMEM;