pnfs-obj: Remove unused variable from objlayout_get_deviceinfo()

Local variable 'sb' was not being used in objlayout_get_deviceinfo().

Signed-off-by: Sachin Bhamare <sbhamare@panasas.com>
Signed-off-by: Boaz Harrosh <bharrosh@panasas.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>