[SCSI] remove scsi_set_device

scsi_add_host is the proper place to set the device, but people copy
the scsi_set_device usage from older drivers again and again.

note that this leaves some legacy drivers like qlogicisp/qlogicfc
without pci association in sysfs, but they're scheduled to go away soon
anyway.

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