pwm: vt8500: Undo preparation of a clock source.

Undo preparation of a clock source if vt8500_pwm_probe() is not
successful.

Signed-off-by: Arvind Yadav <[e-mail]>
Signed-off-by: Thierry Reding <[e-mail]>

drivers/pwm/pwm-vt8500.c

···
 	ret = pwmchip_add(&chip->chip);
 	if (ret < 0) {
 		dev_err(&pdev->dev, "failed to add PWM chip\n");
+		clk_unprepare(chip->clk);
 		return ret;
 	}