iommu: Include linux/err.h

The linux/iommu.h header uses ERR_PTR defined
in linux/err.h but doesn't include it.

Cc:joro@8bytes.org
Reviewed-by: Alex Williamson <alex.williamson@redhat.com>
Signed-off-by: Wang YanQing <udknight@gmail.com>
Signed-off-by: Joerg Roedel <joro@8bytes.org>
diff --git a/include/linux/iommu.h b/include/linux/iommu.h
index ba3b8a9..6a027dc 100644
--- a/include/linux/iommu.h
+++ b/include/linux/iommu.h
@@ -20,6 +20,7 @@
 #define __LINUX_IOMMU_H
 
 #include <linux/errno.h>
+#include <linux/err.h>
 #include <linux/types.h>
 
 #define IOMMU_READ	(1)