iommu/iova: Fix compilation error with !CONFIG_IOMMU_IOVA

commit 201c1db9 upstream.

The stub function for !CONFIG_IOMMU_IOVA needs to be
'static inline'.

Fixes: effa4678

 ('iommu/vt-d: Don't queue_iova() if there is no flush queue')
Signed-off-by: Joerg Roedel <jroedel@suse.de>
Signed-off-by: Dmitry Safonov <dima@arista.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>