arm64: tegra: Update PWM fan node name

According to the device-tree binding document for PWM fans [0], the
PWM fan node name should be 'pwm-fan'. Update the PWM fan node name to
align with this.

[0] Documentation/devicetree/bindings/hwmon/pwm-fan.txt

Signed-off-by: Jon Hunter <jonathanh@nvidia.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>