rbd: remove false error check in getDeviceSize
rbd: remove false error check in getDeviceSize

this removed err condition will be always false as error
is always nil.

Signed-off-by: Humble Chirammal <dc8ba7e82a7df22725dedec9b10c7aaab9ec713f@redhat.com>

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