iommu/vt-d: fix a GCC warning

iommu/vt-d: fix a GCC warning

The commit 6ee1b77ba3ac ("iommu/vt-d: Add svm/sva invalidate function")
introduced a GCC warning,

drivers/iommu/intel-iommu.c:5330:1: warning: 'static' is not at beginning of
declaration [-Wold-style-declaration]
 const static int
 ^~~~~

Fixes: 6ee1b77ba3ac0 ("iommu/vt-d: Add svm/sva invalidate function")
Signed-off-by: Qian Cai <cai@lca.pw>
Acked-by: Lu Baolu <baolu.lu@linux.intel.com>
Link: https://lore.kernel.org/r/20200521215030.16938-1-cai@lca.pw
Signed-off-by: Joerg Roedel <jroedel@suse.de>