pwm: Fix device reference leak

BugLink: http://bugs.launchpad.net/bugs/1650604

commit 0e1614ac upstream.

Make sure to drop the reference to the parent device taken by
class_find_device() after "unexporting" any children when deregistering
a PWM chip.

Fixes: 0733424c ("pwm: Unexport children before chip removal")
Signed-off-by: Johan Hovold <johan@kernel.org>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>

drivers/pwm/sysfs.c

@@ -366,6 +366,8 @@ void pwmchip_sysfs_unexport_children(struct pwm_chip *chip)
 		if (test_bit(PWMF_EXPORTED, &pwm->flags))
 			pwm_unexport_child(parent, pwm);
 	}
+
+	put_device(parent);
 }
 
 static int __init pwm_sysfs_init(void)