pwm: dt: Fix description of second PWM cell

The second cell in the PWM specifier denotes the period in nanoseconds,
not the duty cycle. The latter can be freely configured at runtime and
a PWM with a fixed duty cycle would be rather pointless.
Signed-off-by: Thierry Reding <thierry.reding@avionic-design.de>
Cc: Shawn Guo <shawn.guo@linaro.org>
Cc: Sascha Hauer <s.hauer@pengutronix.de>
Cc: Philipp Zabel <p.zabel@pengutronix.de>
Cc: "Benoît Thébaudeau" <benoit.thebaudeau@advansee.com>
Cc: Stephen Warren <swarren@wwwdotorg.org>
Acked-by: Sascha Hauer <s.hauer@pengutronix.de>
Acked-by: Shawn Guo <shawn.guo@linaro.org>

Documentation/devicetree/bindings/pwm/imx-pwm.txt

@@ -4,7 +4,7 @@ Required properties:
 - compatible: should be "fsl,<soc>-pwm"
 - reg: physical base address and length of the controller's registers
 - #pwm-cells: should be 2.  The first cell specifies the per-chip index
-  of the PWM to use and the second cell is the duty cycle in nanoseconds.
+  of the PWM to use and the second cell is the period in nanoseconds.
 - interrupts: The interrupt for the pwm controller
 
 Example:

Documentation/devicetree/bindings/pwm/mxs-pwm.txt

@@ -4,7 +4,7 @@ Required properties:
 - compatible: should be "fsl,imx23-pwm"
 - reg: physical base address and length of the controller's registers
 - #pwm-cells: should be 2.  The first cell specifies the per-chip index
-  of the PWM to use and the second cell is the duty cycle in nanoseconds.
+  of the PWM to use and the second cell is the period in nanoseconds.
 - fsl,pwm-number: the number of PWM devices
 
 Example:

Documentation/devicetree/bindings/pwm/nvidia,tegra20-pwm.txt

@@ -7,7 +7,7 @@ Required properties:
 - reg: physical base address and length of the controller's registers
 - #pwm-cells: On Tegra the number of cells used to specify a PWM is 2. The
   first cell specifies the per-chip index of the PWM to use and the second
-  cell is the duty cycle in nanoseconds.
+  cell is the period in nanoseconds.
 
 Example: