iommufd/selftest: Make dirty_ops static

The sparse tool complains as follows:

drivers/iommu/iommufd/selftest.c:277:30: warning:
	symbol 'dirty_ops' was not declared. Should it be static?

This symbol is not used outside of selftest.c, so marks it static.

Fixes: 266ce58 ("iommufd/selftest: Test IOMMU_HWPT_ALLOC_DIRTY_TRACKING")
Link: https://patch.msgid.link/r/20240819120007.3884868-1-ruanjinjie@huawei.com
Signed-off-by: Jinjie Ruan <ruanjinjie@huawei.com>
Reviewed-by: Yi Liu <yi.l.liu@intel.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>

drivers/iommu/iommufd/selftest.c

@@ -273,7 +273,7 @@ static int mock_domain_read_and_clear_dirty(struct iommu_domain *domain,
 	return 0;
 }
 
-const struct iommu_dirty_ops dirty_ops = {
+static const struct iommu_dirty_ops dirty_ops = {
 	.set_dirty_tracking = mock_domain_set_dirty_tracking,
 	.read_and_clear_dirty = mock_domain_read_and_clear_dirty,
 };