USB: idmouse: drop redundant open-count check from release

The open count will always be exactly one when release is called, so
drop the redundant sanity check.

Signed-off-by: Johan Hovold <johan@kernel.org>
Link: https://lore.kernel.org/r/20191105103638.4929-3-johan@kernel.org


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>