iommu/omap: Fix error return paths in omap_iommu_attach()

There are couple of issues with the error return paths in
omap_iommu_attach():
1. omap_iommu_attach() returns NULL or ERR_PTR in case of error,
   but omap_iommu_attach_dev() only checks for IS_ERR. Thus a NULL
   return value (in case driver_find_device fails) will cause the
   kernel to panic when omap_iommu_attach_dev() dereferences the
   pointer.
2. A try_module_get() failure returns a valid success value as
   returned from iommu_enable().

Both the above issues have been fixed up to return the proper
ERR_PTR.

Signed-off-by: Florian Vaussard <florian.vaussard@epfl.ch>
Signed-off-by: Suman Anna <s-anna@ti.com>
Signed-off-by: Joerg Roedel <joro@8bytes.org>

drivers/iommu/omap-iommu.c

@@ -863,15 +863,15 @@ static int device_match_by_alias(struct device *dev, void *data)
  **/
 static struct omap_iommu *omap_iommu_attach(const char *name, u32 *iopgd)
 {
-	int err = -ENOMEM;
+	int err;
 	struct device *dev;
 	struct omap_iommu *obj;
 
 	dev = driver_find_device(&omap_iommu_driver.driver, NULL,
 				(void *)name,
 				device_match_by_alias);
 	if (!dev)
-		return NULL;
+		return ERR_PTR(-ENODEV);
 
 	obj = to_iommu(dev);
 
@@ -890,8 +890,10 @@ static struct omap_iommu *omap_iommu_attach(const char *name, u32 *iopgd)
 		goto err_enable;
 	flush_iotlb_all(obj);
 
-	if (!try_module_get(obj->owner))
+	if (!try_module_get(obj->owner)) {
+		err = -ENODEV;
 		goto err_module;
+	}
 
 	spin_unlock(&obj->iommu_lock);