ARM: dts: i.MX27: Remove optional "ptp" clock source for FEC

Patch removes optional "ptp" clock source for FEC. This clock is
missing in i.MX27.
Signed-off-by: Alexander Shiyan <shc_work@mail.ru>
Acked-by: Sascha Hauer <s.hauer@pengutronix.de>
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>

arch/arm/boot/dts/imx27.dtsi

@@ -428,8 +428,8 @@ fec: ethernet@1002b000 {
 				compatible = "fsl,imx27-fec";
 				reg = <0x1002b000 0x4000>;
 				interrupts = <50>;
-				clocks = <&clks 48>, <&clks 67>, <&clks 0>;
-				clock-names = "ipg", "ahb", "ptp";
+				clocks = <&clks 48>, <&clks 67>;
+				clock-names = "ipg", "ahb";
 				status = "disabled";
 			};
 		};