Revert "ceph: fix dentry leak in splice_dentry()"

This reverts commit 8b8f53af.

splice_dentry() is used by three places. For two places, req->r_dentry
is passed to splice_dentry(). In the case of error, req->r_dentry does
not get updated. So splice_dentry() should not drop reference.

Cc: stable@vger.kernel.org # 4.18+
Signed-off-by: "Yan, Zheng" <zyan@redhat.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>