uapi: vduse: fix typo in comment

Fix a spelling mistake in vduse.h: "regsion" → "region" in the
documentation for struct vduse_iova_info.

No functional change.
Signed-off-by: Ashwini Sahu <ashwini@wisig.com>
Message-Id: <20250908095645.610336-1-ashwini@wisig.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>