target: move transport_generic_prepare_cdb into pscsi

The virtual drivers don't need to clear cdb fields they never look at, so move
this code into the pscsi backend.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

diff --cc drivers/target/target_core_pscsi.c
Simple merge

diff --cc drivers/target/target_core_transport.c
Simple merge