ARM: tegra: Provide clock for only one PWM controller

A subsequent patch will add a generic PWM API driver for the Tegra PWFM
controller, supporting all four PWM devices with a single PWM chip. The
device will be named tegra-pwm and only one clock needs to be provided.

Signed-off-by: Thierry Reding <thierry.reding@avionic-design.de>
Signed-off-by: Stephen Warren <swarren@nvidia.com>