scsi: target: Remove unused list 'device_list'

Commit be50f538

 ("target: remove g_device_list") made 'g_device_list'
local as 'device_list' but also removed the last use of it, the code that
added the device to it.

Build tested only.

Signed-off-by: Dr. David Alan Gilbert <linux@treblig.org>
Link: https://lore.kernel.org/r/20240503234419.171823-1-linux@treblig.org
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>