target/loop: depend on SCSI

The target loopback driver is a low-level driver for the SCSI subsystem,
and as such needs to depend on it.

Fixes: 8a39a047 ("target: don't depend on SCSI")
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reported-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

drivers/target/loopback/Kconfig

 config LOOPBACK_TARGET
 	tristate "TCM Virtual SAS target and Linux/SCSI LDD fabric loopback module"
+	depends on SCSI
 	help
 	  Say Y here to enable the TCM Virtual SAS target and Linux/SCSI LLD
 	  fabric loopback module.