drm/mediatek: fix the rate and divder of hdmi phy for MT2701

Due to a clerical error,there is one zero less for 12800000.
Fix it for 128000000
Fixes: 0fc721b2

 ("drm/mediatek: add hdmi driver for MT2701 and MT7623")

Signed-off-by: Wangyan Wang <wangyan.wang@mediatek.com>
Signed-off-by: CK Hu <ck.hu@mediatek.com>