With your board, nothing you can do. The Marvell (so called) SATA III controller cannot provide full SATA III performance that you would get with an Intel SATA III controller, only found on Intel 6 and 7 series chipset boards.
The limitation of the Marvell controller is well known to SSD enthusiasts, and there is no fix for it whatsoever. The speeds you are getting now is the best you can do on the Marvell controller.