ceph: pass cred pointer to ceph_mds_auth_match()

This eliminates a redundant get_current_cred() call, because
ceph_mds_check_access() has already obtained this pointer.

As a side effect, this also fixes a reference leak in
ceph_mds_auth_match(): by omitting the get_current_cred() call, no
additional cred reference is taken.

Cc: stable@vger.kernel.org
Fixes: 596afb0b ("ceph: add ceph_mds_check_access() helper")
Signed-off-by: Max Kellermann <max.kellermann@ionos.com>
Reviewed-by: Xiubo Li <xiubli@redhat.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>