Set the r??_data_len variables before using these instead of after.

This patch fixes the following Coverity complaint:

const: At condition req_data_len != rsp_data_len, the value of req_data_len
must be equal to 0.
const: At condition req_data_len != rsp_data_len, the value of rsp_data_len
must be equal to 0.
dead_error_condition: The condition req_data_len != rsp_data_len cannot be
true.

Cc: Himanshu Madhani <hmadhani@marvell.com>
Fixes: a9b6f722 ("[SCSI] qla2xxx: Implementation of bidirectional.") # v3.7.
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Tested-by: Himanshu Madhani <hmadhani@marvell.com>
Reviewed-by: Himanshu Madhani <hmadhani@marvell.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>