board/ls2080qds: Fix typo in README for QSGMII riser card

DPMACx to PHY mapping for SGMII is mentioned as QSGMII.

So fix typo in README for QSGMII rise card.

Signed-off-by: Prabhakar Kushwaha <prabhakar@freescale.com>
[York Sun: Change from ls2085aqds to ls2080aqds]
Reviewed-by: York Sun <yorksun@freescale.com>