ARM: dts: omap4: add twd clock to DT

Booting Linux 3.14 on Pandaboard currently gets the following
message displayed:

smp_twd: clock not found -2

Define "mpu_periphclk" as the twd clock in omap4 dts to avoid this.
Signed-off-by: Gilles Chanteperdrix <gilles.chanteperdrix@xenomai.org>
Acked-by: Tero Kristo <t-kristo@ti.com>
Signed-off-by: Tero Kristo <t-kristo@ti.com>

arch/arm/boot/dts/omap4.dtsi

@@ -67,6 +67,7 @@ L2: l2-cache-controller@48242000 {
 
 	local-timer@48240600 {
 		compatible = "arm,cortex-a9-twd-timer";
+		clocks = <&mpu_periphclk>;
 		reg = <0x48240600 0x20>;
 		interrupts = <GIC_PPI 13 (GIC_CPU_MASK_RAW(3) | IRQ_TYPE_LEVEL_HIGH)>;
 	};