bcache: fix typo in code comments of closure_return_with_destructor()

The code comments of closure_return_with_destructor() in closure.h makrs
function name as closure_return(). This patch fixes this type with the
correct name - closure_return_with_destructor.

Signed-off-by: Coly Li <colyli@suse.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>