ARM: dts: imx: Add missing #phy-cells to usb-nop-xceiv

"usb-nop-xceiv" is using the phy binding, but is missing #phy-cells
property. This is probably because the binding was the precursor to the phy
binding.

Fixes the following warning in i.MX dts files:

Warning (phys_property): Missing property '#phy-cells' in node ...

Signed-off-by: Rob Herring <robh@kernel.org>
Cc: Sascha Hauer <kernel@pengutronix.de>
Cc: Fabio Estevam <fabio.estevam@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>
diff --git a/arch/arm/boot/dts/imx51.dtsi b/arch/arm/boot/dts/imx51.dtsi
index 378be72..00d30bd 100644
--- a/arch/arm/boot/dts/imx51.dtsi
+++ b/arch/arm/boot/dts/imx51.dtsi
@@ -113,6 +113,7 @@
 			reg = <0>;
 			clocks = <&clks IMX5_CLK_USB_PHY_GATE>;
 			clock-names = "main_clk";
+			#phy-cells = <0>;
 		};
 	};