[][kernel][common][pwm][Remove unused clock-cells in pwm dts]

[Description]
Remove unused clock-cells in pwm dts.
PWM is not a clock provider and its binding doesn't specify
"#clock-cells" property in "mediatek,mt2712-pwm.yaml".

[Release-log]
N/A

Change-Id: I983388dd47547315d8c704dad703544638200590
Reviewed-on: https://gerrit.mediatek.inc/c/openwrt/feeds/mtk_openwrt_feeds/+/8521724
2 files changed