USB: serial, use tty_standard_install

But before that we need to reorder the calls so that we don't need to
lower the reference counts if usb_autopm_get_interface fails.

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Cc: Alan Cox <alan@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>