arch/x86/kernel: Add missing spin_unlock

commit 84fe6c19 upstream.

Add a spin_unlock missing on the error path.  The locks and unlocks are
balanced in other functions, so it seems that the same should be the case
here.

The semantic match that finds this problem is as follows:
(http://coccinelle.lip6.fr/)

// <smpl>
@@
expression E1;
@@

* spin_lock(E1,...);
  <+... when != E1
  if (...) {
    ... when != E1
*   return ...;
  }
  ...+>
* spin_unlock(E1,...);
// </smpl>
Signed-off-by: Julia Lawall <julia@diku.dk>
Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

arch/x86/kernel/amd_iommu.c

@@ -1420,6 +1420,7 @@ static int __attach_device(struct device *dev,
 			   struct protection_domain *domain)
 {
 	struct iommu_dev_data *dev_data, *alias_data;
+	int ret;
 
 	dev_data   = get_dev_data(dev);
 	alias_data = get_dev_data(dev_data->alias);
@@ -1431,13 +1432,14 @@ static int __attach_device(struct device *dev,
 	spin_lock(&domain->lock);
 
 	/* Some sanity checks */
+	ret = -EBUSY;
 	if (alias_data->domain != NULL &&
 	    alias_data->domain != domain)
-		return -EBUSY;
+		goto out_unlock;
 
 	if (dev_data->domain != NULL &&
 	    dev_data->domain != domain)
-		return -EBUSY;
+		goto out_unlock;
 
 	/* Do real assignment */
 	if (dev_data->alias != dev) {
@@ -1453,10 +1455,14 @@ static int __attach_device(struct device *dev,
 
 	atomic_inc(&dev_data->bind);
 
+	ret = 0;
+
+out_unlock:
+
 	/* ready */
 	spin_unlock(&domain->lock);
 
-	return 0;
+	return ret;
 }
 
 /*