dt-bindings: iio: update STM32 timers clock names

Clock name has been updated during driver/DT binding review:
https://lkml.org/lkml/2016/12/13/718
Update DT binding doc to reflect this.

Fixes: bf2d8581b1b3 (iio: Add bindings for STM32 timer trigger driver)
Signed-off-by: Fabrice Gasnier <fabrice.gasnier@st.com>
Acked-by: Benjamin Gaignard <benjamin.gaignard@linaro.org>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

Documentation/devicetree/bindings/iio/timer/stm32-timer-trigger.txt

@@ -14,7 +14,7 @@ Example:
 		compatible = "st,stm32-timers";
 		reg = <0x40010000 0x400>;
 		clocks = <&rcc 0 160>;
-		clock-names = "clk_int";
+		clock-names = "int";
 
 		timer@0 {
 			compatible = "st,stm32-timer-trigger";