hsail: Get rid of an inert private member of StorageSpace.

The "segment" private element in this class was only ever set to zero
on construction, and then used to index into a list of segment names
to get the string "none" in a DPRINTF. If debugging was turned off,
there would be no consumers of that variable, and that upset g++. This
change removes the essentially useless variable, and also that bit of
text in the DPRINTF.

Change-Id: I3f85db4af5f0678768243daf84b8d698350af931
Reviewed-on: https://gem5-review.googlesource.com/9221
Reviewed-by: Anthony Gutierrez <anthony.gutierrez@amd.com>
Maintainer: Anthony Gutierrez <anthony.gutierrez@amd.com>

gpu-compute: AMD's baseline GPU model