Fix mpr device mapper fallback logic for busses with multiple expanders.
r308217 added fallback logic for mpr's device mapper, to be used in case the
card's nonvolatile mapping table is corrupt. The fallback logic simply uses a
device's phy number as its SCSI target id. But this doesn't work on SAS busses
with multiple expanders, because phy numbers are only unique per-expander.
Change the fallback logic to use a combination of the Enclosure Handle and