scsi: target: Reset t_task_cdb pointer in error case

In the Linux kernel, the following vulnerability has been resolved: scsi: target: Reset t_task_cdb pointer in error case If allocation of cmd->t_task_cdb fails, it remains NULL but is later dereferenced in the 'err' path. In case of error, reset NULL t_task_cdb value to point at the default fixed-size buffer. Found by Linux Verification Center (linuxtesting.org) with SVACE.