cuse: fix memory leak

The problem is that fuse_dev_alloc() acquires an extra reference to cc.fc,
and the original ref count is never dropped.

Reported-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Miklos Szeredi <miklos@szeredi.hu>
Fixes: cc080e9e9be1 ("fuse: introduce per-instance fuse_dev structure")
Cc: <stable@vger.kernel.org> # v4.2+
static ssize_t cuse_class_abort_store(struct device *dev,
				      struct device_attribute *attr,
				      const char *buf, size_t count)
{
	struct cuse_conn *cc = dev_get_drvdata(dev);

	fuse_abort_conn(&cc->fc);
	return count;
}

static ssize_t cuse_class_abort_store(struct device *dev,
				      struct device_attribute *attr,
				      const char *buf, size_t count)
{
	struct cuse_conn *cc = dev_get_drvdata(dev);

	fuse_abort_conn(&cc->fc);
	return count;
}
