sierra: Fix formatting

Andrew Morton wrote:

in drivers/usb/serial/sierra.c:

        } else {
                if (urb->actual_length) {
+               tty = tty_port_tty_get(&port->port);
                        tty_buffer_request_room(tty, urb->actual_length);

it's missing a tab.
Signed-off-by: Alan Cox <alan@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>