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.

Fixes: 9e95fb8 ("scsi: target: Fix NULL pointer dereference")
Cc: stable@vger.kernel.org
Signed-off-by: Andrey Vatoropin <a.vatoropin@crpt.ru>
Reviewed-by: Mike Christie <michael.christie@oracle.com>
Link: https://patch.msgid.link/20251118084014.324940-1-a.vatoropin@crpt.ru
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

Author: Andrey Vatoropin

drivers/target/target_core_transport.c

@@ -1524,6 +1524,7 @@ target_cmd_init_cdb(struct se_cmd *cmd, unsigned char *cdb, gfp_t gfp)
 	if (scsi_command_size(cdb) > sizeof(cmd->__t_task_cdb)) {
 		cmd->t_task_cdb = kzalloc(scsi_command_size(cdb), gfp);
 		if (!cmd->t_task_cdb) {
+			cmd->t_task_cdb = &cmd->__t_task_cdb[0];
 			pr_err("Unable to allocate cmd->t_task_cdb"
 				" %u > sizeof(cmd->__t_task_cdb): %lu ops\n",
 				scsi_command_size(cdb),