rbd: correct upstream kernel version for deep-flatten
rbd: correct upstream kernel version for deep-flatten

as v5.1.0 supports the deep-flatten feature,lowering
the required version to map rbd images which
are having deep-flatten feature

Signed-off-by: Madhu Rajanna <60fbf37a92c2a0908e31296d18dadbec5a4dae17@gmail.com>

ceph/ceph-csi,ceph/ceph-csi,ceph/ceph-csi,ceph/ceph-csi