[SCSI] tgt: use KMEM_CACHE macro
This uses new KMEM_CACHE() macro instead of kmem_cache_create directly
to simplify slab cache creation.
Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>