dt: pwm: bcm2835: fix typo in clocks property name

According to the examples of BCM2835 PWM device nodes there is a typo in
'clocks' property name, which is a common property name on clock consumer
side to store a phandle to an input clock.
Signed-off-by: Vladimir Zapolskiy <vz@mleia.com>
Signed-off-by: Rob Herring <robh@kernel.org>

Documentation/devicetree/bindings/pwm/pwm-bcm2835.txt

@@ -3,7 +3,7 @@ BCM2835 PWM controller (Raspberry Pi controller)
 Required properties:
 - compatible: should be "brcm,bcm2835-pwm"
 - reg: physical base address and length of the controller's registers
-- clock: This clock defines the base clock frequency of the PWM hardware
+- clocks: This clock defines the base clock frequency of the PWM hardware
   system, the period and the duty_cycle of the PWM signal is a multiple of
   the base period.
 - #pwm-cells: Should be 2. See pwm.txt in this directory for a description of