powerpc/iommu: Use permission-specific DEVICE_ATTR variants

Use DEVICE_ATTR_RW for read-write attributes.  This simplifies the
source code, improves readbility, and reduces the chance of
inconsistencies.
Signed-off-by: Julia Lawall <Julia.Lawall@lip6.fr>
Acked-by: Michael Ellerman <mpe@ellerman.id.au> (powerpc)
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/kernel/iommu.c

@@ -127,8 +127,7 @@ static ssize_t fail_iommu_store(struct device *dev,
 	return count;
 }
 
-static DEVICE_ATTR(fail_iommu, S_IRUGO|S_IWUSR, fail_iommu_show,
-		   fail_iommu_store);
+static DEVICE_ATTR_RW(fail_iommu);
 
 static int fail_iommu_bus_notify(struct notifier_block *nb,
 				 unsigned long action, void *data)