scsi: ch: Have midlayer retry ch_do_scsi() UAs

ch_do_scsi(scsi_changer *ch, unsigned char *cmd, int cmd_len,

	   void *buffer, unsigned int buflength, enum req_op op)

{

	int errno, retries = 0, timeout, result;

	int errno = 0, timeout, result;

	struct scsi_sense_hdr sshdr;

	struct scsi_failure failure_defs[] = {

		{

			.sense = UNIT_ATTENTION,

			.asc = SCMD_FAILURE_ASC_ANY,

			.ascq = SCMD_FAILURE_ASCQ_ANY,

			.allowed = 3,

			.result = SAM_STAT_CHECK_CONDITION,

		},

		{}

	};

	struct scsi_failures failures = {

		.failure_definitions = failure_defs,

	};

	const struct scsi_exec_args exec_args = {

		.sshdr = &sshdr,

		.failures = &failures,

	};

	timeout = (cmd[0] == INITIALIZE_ELEMENT_STATUS)

		? timeout_init : timeout_move;

 retry:

	errno = 0;

	result = scsi_execute_cmd(ch->device, cmd, op, buffer, buflength,

				  timeout * HZ, MAX_RETRIES, &exec_args);

	if (result < 0)

		if (debug)

			scsi_print_sense_hdr(ch->device, ch->name, &sshdr);

		errno = ch_find_errno(&sshdr);

		switch(sshdr.sense_key) {

		case UNIT_ATTENTION:

			if (retries++ < 3)

				goto retry;

			break;

		}

	}

	return errno;

}