backlight: grab ops_lock before testing bd->ops

According to the comment describing ops_lock in the definition of struct
backlight_device and when comparing with other functions in backlight.c
the mutex must be hold when checking ops to be non-NULL.

Fixes a problem added by c835ee7f ("backlight: Add suspend/resume
support to the backlight core") in Jan 2009.
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Acked-by: Richard Purdie <rpurdie@linux.intel.com>
Cc: <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/video/backlight/backlight.c

@@ -197,12 +197,12 @@ static int backlight_suspend(struct device *dev, pm_message_t state)
 {
 	struct backlight_device *bd = to_backlight_device(dev);
 
-	if (bd->ops->options & BL_CORE_SUSPENDRESUME) {
 	mutex_lock(&bd->ops_lock);
+	if (bd->ops && bd->ops->options & BL_CORE_SUSPENDRESUME) {
 		bd->props.state |= BL_CORE_SUSPENDED;
 		backlight_update_status(bd);
-		mutex_unlock(&bd->ops_lock);
 	}
+	mutex_unlock(&bd->ops_lock);
 
 	return 0;
 }
@@ -211,12 +211,12 @@ static int backlight_resume(struct device *dev)
 {
 	struct backlight_device *bd = to_backlight_device(dev);
 
-	if (bd->ops->options & BL_CORE_SUSPENDRESUME) {
 	mutex_lock(&bd->ops_lock);
+	if (bd->ops && bd->ops->options & BL_CORE_SUSPENDRESUME) {
 		bd->props.state &= ~BL_CORE_SUSPENDED;
 		backlight_update_status(bd);
-		mutex_unlock(&bd->ops_lock);
 	}
+	mutex_unlock(&bd->ops_lock);
 
 	return 0;
 }