ceph: Fix incorrect statfs report for small quota

ceph: Fix incorrect statfs report for small quota

Problem:
The statfs reports incorrect free/available space
for quota less then CEPH_BLOCK size (4M).

Solution:
For quota less than CEPH_BLOCK size, smaller block
size of 4K is used. But if quota is less than 4K,
it is decided to go with binary use/free of 4K
block. For quota size less than 4K size, report the
total=used=4K,free=0 when quota is full and
total=free=4K,used=0 otherwise.

Signed-off-by: Kotresh HR <khiremat@redhat.com>
Signed-off-by: Jeff Layton <jlayton@kernel.org>