pwm: tiehrpwm: fix clock imbalance in probe error path

Make sure to unprepare the clock before returning on late probe errors.

Fixes: b388f15f ("pwm: pwm-tiehrpwm: Use clk_enable/disable instead clk_prepare/unprepare.")
Signed-off-by: Johan Hovold <johan@kernel.org>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>