ARM: dts: bcm958625-meraki-mx6x: Use #pwm-cells = <3>

ARM: dts: bcm958625-meraki-mx6x: Use #pwm-cells = <3>

bcm-nsp.dtsi has #pwm-cells = <3> as is specified in the binding. So to
also use that correct value for bcm958625-meraki-mx6x the property
overriding that value just has to be dropped. This fixes a few warnings
like:

	arch/arm/boot/dts/broadcom/bcm958625-meraki-mx65.dtb: pwm@31000: #pwm-cells: 3 was expected
		from schema $id: http://devicetree.org/schemas/pwm/brcm,iproc-pwm.yaml#

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@baylibre.com>
Link: https://lore.kernel.org/r/20250527181320.373572-2-u.kleine-koenig@baylibre.com
Signed-off-by: Florian Fainelli <florian.fainelli@broadcom.com>