[SCSI] fix two leaks in scsi_alloc_sdev failure paths

If the scsi_alloc_queue or the slave_alloc calls in scsi_alloc_device fail,
we forget to release the locally allocated sdev on the failure path.

Coverity #609

Signed-off-by: Dave Jones <davej@redhat.com>
Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>