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: NJohan Hovold <johan@kernel.org>
Signed-off-by: NThierry Reding <thierry.reding@gmail.com>