fuse: remove unneeded atomic set in uring creation

When the ring is allocated, it is kzalloc-ed. ring->queue_refs will
already be initialized to 0 by default. It does not need to be
atomically set to 0.

Signed-off-by: Joanne Koong <joannelkoong@gmail.com>
Reviewed-by: Bernd Schubert <bschubert@ddn.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>