USB: double put_tty_driver(gs_tty_driver) in gserial_setup()

If the driver cannot be registered, put_tty_driver(gs_tty_driver)
occurred here as well as at label fail.

put_tty_driver() already occurs at label fail

Signed-off-by: Roel Kluin <roel.kluin@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>