phy: lynx-10g: remove the 'not tested' comment from 'fsl,ls2088a-serdes1'

commit  55dab2ec82591e93de3319a89c23e0ae5829b664 from
https://github.com/nxp-imx/linux-imx lf-6.1.y

The 'fsl,ls2088a-serdes1' compatible handling was tested in a copper
backplane scenario. Remove the comment saying otherwise.

Signed-off-by: Ioana Ciornei <ioana.ciornei@nxp.com>
Signed-off-by: Xiaolei Wang <xiaolei.wang@windriver.com>