libsas: fix sas_get_port_device regression

libsas: fix sas_get_port_device regression

Commit 899fcf4 "[SCSI] libsas: set attached device type and target
protocols for local phys" setup 'phy' to be dereferenced after
list_for_each_entry(phy, &port->phy_list, port_phy_el) (i.e. phy ==
&port->phy_list) resulting in reports like:

  BUG: unable to handle kernel NULL pointer dereference at 00000000000002b0
  IP: [<ffffffffa00ce948>] sas_discover_domain+0x29e/0x4fb [libsas]

...fix by deferring sas_phy_set_target() to the end of
sas_get_port_device().

Reported-by: Tom Jackson <thomas.p.jackson@intel.com>
Tested-by: Tom Jackson <thomas.p.jackson@intel.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>