ceph: use 2 instead of 1 as fallback for 32-bit inode number

The root directory of the Ceph mount has inode number 1, so falling back
to 1 always creates a collision. 2 is unused on my test systems and seems
less likely to collide.

Signed-off-by: Amon Ott <ao@m-privacy.de>
Signed-off-by: Sage Weil <sage@newdream.net>