[SCSI] mptsas: eliminate ghost devices

One of the current problems the mptsas driver has is that of "ghost"
devices (these are devices the firmware reports as existing, but what
they actually represent are the parents of a lower device), so for
example in my dual expander configuration, three expanders actually show
up, two for the real expanders but a third is created because the
firmware reports that the lower expander also has another expander
connected (which is simply the port going back to the upper expander).

The attached patch eliminates all these ghosts by not allocating any
devices for them if the SAS address is the SAS address of the parent.

Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>