pwm: atmel-pwm: Do not unprepare clock after successful registration

When the PWM controller is registered successfully, the clock can not
unprepare, so fix it.

Signed-off-by: Bo Shen <voice.shen@atmel.com>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>
diff --git a/drivers/pwm/pwm-atmel.c b/drivers/pwm/pwm-atmel.c
index 657e90a..bf4144a 100644
--- a/drivers/pwm/pwm-atmel.c
+++ b/drivers/pwm/pwm-atmel.c
@@ -362,6 +362,8 @@
 
 	platform_set_drvdata(pdev, atmel_pwm);
 
+	return ret;
+
 unprepare_clk:
 	clk_unprepare(atmel_pwm->clk);
 	return ret;