target: Fix cmd size for PR-OUT in passthrough_parse_cdb

The cmd size should be 4bytes form byte5 to byte8 when CDB opcode
is PERSISTENT_RESERVE_OUT in SPC3 and SPC4

(Also fix up the same in spc_parse_cdb - MNC)

Signed-off-by: Tang Wenji <tang.wenji@zte.com.cn>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>