[SCSI] SCSI osst: add error handling to module init, sysfs

- check all sysfs-related return codes, and propagate them back to callers

- properly unwind errors in osst_probe(), init_osst().  This fixes a
  leak that occured if scsi driver registration failed, and fixes an
  oops if sysfs creation returned an error.

(unrelated)
- kzalloc() cleanup in new_tape_buf()

Signed-off-by: Jeff Garzik <jeff@garzik.org>
Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>