iommu-api: Add missing header file

If CONFIG_IOMMU_API is not defined some functions will just
return -ENODEV. Add errno.h for the definition of ENODEV.
Signed-off-by: Laura Abbott <lauraa@codeaurora.org>
Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>

include/linux/iommu.h

@@ -19,6 +19,8 @@
 #ifndef __LINUX_IOMMU_H
 #define __LINUX_IOMMU_H
 
+#include <linux/errno.h>
+
 #define IOMMU_READ	(1)
 #define IOMMU_WRITE	(2)
 #define IOMMU_CACHE	(4) /* DMA cache coherency */