scsi_send_eh_cmnd is the last user of non-sg commands currently.
This patch switches it to a one-element SG list.  Also updates the
kerneldoc comment for scsi_send_eh_cmnd to reflect reality while we're
at it.

Test on my mptsas card, but this should get testing with as many
drivers as possible.
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Signed-off-by: NJames Bottomley <James.Bottomley@SteelEye.com>