[SCSI] SCSI megaraid_sas: handle thrown errors

- handle clear_user() error

- handle and properly unwind from sysfs errors thrown during mod init

- adjust order of calls in megasas_exit() to precisely match
  registration order in megasas_init()

Signed-off-by: Jeff Garzik <jeff@garzik.org>

Updated for extra attribute and
Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>