scsi: osd_uld: Check scsi_device_get() return value

scsi_device_get() can fail. Hence check its return value.

Signed-off-by: Bart Van Assche <bart.vanassche@sandisk.com>
Cc: Boaz Harrosh <bharrosh@panasas.com>
Acked-by: Boaz Harrosh <ooo@electrozaur.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>