USB: legousbtower: clean up pointer declarations in driver data

Clean up the pointer declarations in the driver data, whose style wasn't
even consistent with the rest of the driver.

Signed-off-by: Johan Hovold <johan@kernel.org>
Link: https://lore.kernel.org/r/20191105084152.16322-10-johan@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>