target: Drop left-over PHBA_PDEV set attr checks

Now that PSCSI is only exposing four hw_* read-only device attributes,
go ahead and drop the left-over -> legacy PHBA_PDEV checks in various
se_dev_set_* code, since it's now only used by virtual devices.

Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>