misc: ls2_sfp: Fix regulator name

Unlike in Linux, -supply is not automatically appended to regulator
requests. Add it.

Fixes: 2645bc0e ("arm: layerscape: Add sfp driver")
Signed-off-by: Sean Anderson <sean.anderson@seco.com>
Signed-off-by: Peng Fan <peng.fan@nxp.com>