ARM: dts: imx51-zii-rdu1: Add missing #phy-cells to usb-nop-xceiv

Commit 915fbe59

 ("ARM: dts: imx: Add missing #phy-cells to
usb-nop-xceiv") missed to update imx51-zii-rdu1.dts probably due to a
merge timing issue, so add #phy-cells here too.

Signed-off-by: Fabio Estevam <fabio.estevam@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>